PR26844: fix off-by-one error when copying printed backtraces

PR26844: fix off-by-one error when copying printed backtraces

Since log->buf isn't null-terminated, log->len represents the total
number of bytes present in the log buffer for copying. The use of
strlcpy() here with log->len as its size results in log->len - 1 bytes
being copied, with the log->len'nth byte of the output buffer being set
to zero to terminate the string. Use memcpy() instead to remedy this,
while ensuring that the output buffer has space for null termination,
since the output buffer needs to be terminated.