Fixed 'memleak' detected by cppcheck

[kostyk348]

In terms of curiosity run cppcheck on alpaca.cpp and got that message:

Checking chat.cpp ...
chat.cpp:564:9: error: Common realloc mistake: 'buf' nulled but not freed upon failure [memleakOnRealloc]
buf = realloc(buf, buf_size);
^
Checking chat.cpp: _WIN32...
Checking chat.cpp: _WIN32;APPLE;MACH;unix...
Checking chat.cpp: APPLE;MACH;unix...
Checking chat.cpp: __ARM_NEON...

Nothing serious I guess, but now there's no errors and everything builds ok

[michieal]

Here's an alternate way to handle it, if you like it better. I saw the memleak in cppcheck too, and I fixed it on my end before coming across this. Seeing it, I thought that I could share my code too, and people would have options. (I don't really think that it matters which one a person goes with, as they both do effectively the same thing.)

	void* old_buffer = buf;

        // reallocate
        buf_size = buf_size_new;
        buf = realloc(buf, buf_size);
        if (buf == nullptr) {
            fprintf(stderr, "%s: failed to allocate %zu bytes\n", __func__, buf_size);
	    free(old_buffer); // prevent memory leakage.
            return false;
        }
    }