Avoid buffer overflow in Log.

[f1rmb]

Avoid possible buffer overflow.
Fix instant crashing when compiled and run on LinuxMint (GCC 13.3) and probably many distro with recent toolchain. It seems I'm not the only one experiencing this problem:

*** buffer overflow detected ***: terminated
Aborted (core dumped)

It's identical to #811.

[g4klx]

Before I make changes, I want to know what log message is causing this error. I don't normally generate long log messages, so what is it trying to log? Please show me.

[f1rmb]

It's not a matter of log message, it's purely a possible buffer overflow, handled at run time.

::vsnprintf(buffer + ::strlen(buffer), 500, fmt, vl);

is wrong, as passed buffer is NOT &buffer[0], but &buffer[::strlen(buffer)], hence the vsnprintf max length argument is overflowing the buffer by ::strlen(buffer).

Older GCC and libs don't check for this bug, new ones does.

[f1rmb]

Also, when compiled with my GCC 13, the code abort() before any logging message is displayed/logged, as that happens when vsnprintf() is called.