Fix Coverity Scan CID 300471 (Using uninitialized value queue->mutex when calling free.)

openair2/ENB_APP/flexran_agent_task_manager.c

@@ -77,6 +77,7 @@ flexran_agent_task_queue_t *flexran_agent_task_queue_init(mid_t mod_id, size_t c
   if (queue == NULL)
     goto error;
 
+  queue->mutex = NULL;
   /* If no comparator was given, use the default one */
   if (cmp == NULL)
     queue->cmp = _flexran_agent_task_queue_cmp;