issue in Helpers::GetTTDDirectory

Repro:
ChakraCore/BuildLinux/Release/ch -

==28834==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000ef84 at pc 0x564b52e06139 bp 0x7fffa452de30 sp 0x7fffa452de28
READ of size 2 at 0x60200000ef84 thread T0
    #0 0x564b52e06138 in Helpers::GetTTDDirectory(char16_t const*, unsigned long*, unsigned char*) (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x347138)
    #1 0x564b52dfdbb0 in main (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x33ebb0)
    #2 0x7f724d7df82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #3 0x564b52d267a8 in _start (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x2677a8)

0x60200000ef84 is located 12 bytes to the left of 16-byte region [0x60200000ef90,0x60200000efa0)
allocated by thread T0 here:
    #0 0x564b52df8050 in operator new[](unsigned long) (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x339050)
    #1 0x564b52dfd8a9 in main (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x33e8a9)
    #2 0x7f724d7df82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)

SUMMARY: AddressSanitizer: heap-buffer-overflow (/home/fuzzer/browsers/ChakraCore/BuildLinux/Release/ch+0x347138) in Helpers::GetTTDDirectory(char16_t const*, unsigned long*, unsigned char*)
Shadow bytes around the buggy address:
  0x0c047fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9de0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa 04 fa
=>0x0c047fff9df0:[fa]fa 00 00 fa fa fd fd fa fa 04 fa fa fa 00 fa
  0x0c047fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07 
  Heap left redzone:       fa
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==28834==ABORTING