Fixed Bug #63581 Possible buffer overflow

Fixed Bug #63581 Possible buffer overflow

In fpm-log, possible buffer overflow. Check for length is done at
the beginning of the loop, so is not done when overflow occurs
on the last loop (len = 1024 or 1025). (ack from fat).

This issue where found from by static code analysis tool and, so,
I can't provide any reproducer.