Fix FreeDV Reporter crash when sending RX record.

[tmiw]

Resolves very intermittent crash when receiving RX records. On my M1 Mac, the crash log for this issue looked like the following:

Thread 15 Crashed:
0   libsystem_platform.dylib      	       0x19b50e7fc _platform_memmove + 444
1   libc++.1.dylib                	       0x19b40fa24 std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>::basic_string(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&) + 64
2   FreeDV                        	       0x102c4608c sio::string_message::string_message(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&) + 76 (sio_message.h:202)
3   FreeDV                        	       0x102c45ffc sio::string_message::string_message(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&) + 36 (sio_message.h:203)
4   FreeDV                        	       0x102c45ec8 sio::string_message::create(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&) + 44 (sio_message.h:213)
5   FreeDV                        	       0x102c423bc sio::object_message::insert(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>> const&) + 44 (sio_message.h:359)
6   FreeDV                        	       0x102c55338 FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1::operator()() const + 124 (FreeDVReporter.cpp:120)
7   FreeDV                        	       0x102c552b0 decltype(std::declval<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1&>()()) std::__1::__invoke[abi:v15006]<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1&>(FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1&) + 24 (invoke.h:394)
8   FreeDV                        	       0x102c55268 void std::__1::__invoke_void_return_wrapper<void, true>::__call<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1&>(FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1&) + 24 (invoke.h:479)
9   FreeDV                        	       0x102c55244 std::__1::__function::__alloc_func<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1, std::__1::allocator<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1>, void ()>::operator()[abi:v15006]() + 28 (function.h:185)
10  FreeDV                        	       0x102c53ff8 std::__1::__function::__func<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1, std::__1::allocator<FreeDVReporter::addReceiveRecord(std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, unsigned long long, char)::$_1>, void ()>::operator()() + 28 (function.h:359)
11  FreeDV                        	       0x102bb2b9c std::__1::__function::__value_func<void ()>::operator()[abi:v15006]() const + 68 (function.h:512)
12  FreeDV                        	       0x102bb2b4c std::__1::function<void ()>::operator()() const + 24 (function.h:1197)
13  FreeDV                        	       0x102c41f74 FreeDVReporter::threadEntryPoint_() + 356 (FreeDVReporter.cpp:434)
14  FreeDV                        	       0x102c4c568 decltype(*std::declval<FreeDVReporter*&>().*std::declval<void (FreeDVReporter::*&)()>()()) std::__1::__invoke[abi:v15006]<void (FreeDVReporter::*&)(), FreeDVReporter*&, void>(void (FreeDVReporter::*&)(), FreeDVReporter*&) + 116 (invoke.h:359)
15  FreeDV                        	       0x102c4c4e8 std::__1::__bind_return<void (FreeDVReporter::*)(), std::__1::tuple<FreeDVReporter*>, std::__1::tuple<>, __is_valid_bind_return<void (FreeDVReporter::*)(), std::__1::tuple<FreeDVReporter*>, std::__1::tuple<>>::value>::type std::__1::__apply_functor[abi:v15006]<void (FreeDVReporter::*)(), std::__1::tuple<FreeDVReporter*>, 0ul, std::__1::tuple<>>(void (FreeDVReporter::*&)(), std::__1::tuple<FreeDVReporter*>&, std::__1::__tuple_indices<0ul>, std::__1::tuple<>&&) + 60 (bind.h:263)
16  FreeDV                        	       0x102c4c4a0 std::__1::__bind_return<void (FreeDVReporter::*)(), std::__1::tuple<FreeDVReporter*>, std::__1::tuple<>, __is_valid_bind_return<void (FreeDVReporter::*)(), std::__1::tuple<FreeDVReporter*>, std::__1::tuple<>>::value>::type std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>::operator()[abi:v15006]<>() + 36 (bind.h:295)
17  FreeDV                        	       0x102c4c448 decltype(std::declval<std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>>()()) std::__1::__invoke[abi:v15006]<std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>>(std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>&&) + 24 (invoke.h:394)
18  FreeDV                        	       0x102c4c424 void std::__1::__thread_execute[abi:v15006]<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>>(std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>>&, std::__1::__tuple_indices<>) + 28 (thread:290)
19  FreeDV                        	       0x102c4c12c void* std::__1::__thread_proxy[abi:v15006]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, std::__1::__bind<void (FreeDVReporter::*)(), FreeDVReporter*>>>(void*) + 84 (thread:301)
20  libsystem_pthread.dylib       	       0x19b4dffa8 _pthread_start + 148
21  libsystem_pthread.dylib       	       0x19b4dada0 thread_start + 8

I suspect some on Windows and Linux were running into similar as well.