fix segfault

libs/apr/threadproc/unix/thread.c

@@ -175,7 +175,7 @@ APR_DECLARE(apr_status_t) apr_thread_create(apr_thread_t **new,
 
     if ((stat = pthread_create((*new)->td, temp, dummy_worker, (*new))) == 0) {
 #ifndef __APPLE__
-		if (attr->priority) {
+		if (attr && attr->priority) {
 			pthread_t *thread = (*new)->td;
 			pthread_setschedprio(*thread, attr->priority);
 		}