lock: Avoid some undefined behaviour when freeing mutexes.

changes/bug31736

src/app/config/config.c

src/feature/relay/router.c

src/lib/crypt_ops/crypto_openssl_mgt.c

src/lib/lock/compat_mutex.c

src/lib/lock/compat_mutex_pthreads.c

src/lib/thread/compat_threads.c

src/lib/thread/threads.h