Fix end-case on comm failure.

src/common/slurm_protocol_api.c

@@ -1394,7 +1394,7 @@ int slurm_send_recv_controller_msg(slurm_msg_t *req, slurm_msg_t *resp)
 			slurm_free_cred(resp->cred);
 
 		rc = errno;
-		if(list_count(ret_list)>0) {
+		if(ret_list && (list_count(ret_list)>0)) {
 			error("We didn't do things correctly "
 			      "missed %d responses",
 			      list_count(ret_list));