linuxthreads.old: fix crash in debug code
linuxthreads.old: fix crash in debug code

If pthread_join() is called and there is nothing to join, then the debug
code will attempt to dereference a NULL pointer.

Signed-off-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@gentoo.org>

joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc