Correctly handle the race itself, too (don't leave it locked).

This is about to be replaced anyway by initialization explicitly
instead of lazily, and reducing the complexity of it.  As it is
now, this will work fine, however.

lib/libc/stdio/_flock_stub.c

@@ -99,6 +99,7 @@ init_lock(FILE *fp)
 		}
 		if (fp->_lock != NULL) {	/* lost the race */
 			free(p);
+			_pthread_mutex_unlock(&init_lock_mutex);
 			return (0);
 		}
 		fp->_lock = p;