mdns: fix static analysis warnings

* Original commit: espressif/esp-idf@c34de4c

Author: david-cermak

components/mdns/mdns.c

@@ -1312,6 +1312,7 @@ static mdns_tx_packet_t * _mdns_create_probe_packet(tcpip_adapter_if_t tcpip_if,
         q->domain = MDNS_DEFAULT_DOMAIN;
         if (!q->host || _mdns_question_exists(q, packet->questions)) {
             free(q);
+            continue;
         } else {
             queueToEnd(mdns_out_question_t, packet->questions, q);
         }
@@ -2801,7 +2802,7 @@ void mdns_parse_packet(mdns_rx_packet_t * packet)
                         col = 1;
                     } else if (!clas) {
                         col = -1;
-                    } else {
+                    } else if (service) { // only detect srv collision if service existed
                         col = _mdns_check_srv_collision(service->service, priority, weight, port, name->host, name->domain);
                     }
                     if (col && (parsed_packet->probe || parsed_packet->authoritative)) {
@@ -3831,23 +3832,25 @@ static void _mdns_execute_action(mdns_action_t * action)
         break;
     case ACTION_SERVICE_DEL:
         a = _mdns_server->services;
-        if (_mdns_server->services == action->data.srv_del.service) {
-            _mdns_server->services = a->next;
-            _mdns_send_bye(&a, 1, false);
-            _mdns_remove_scheduled_service_packets(a->service);
-            _mdns_free_service(a->service);
-            free(a);
-        } else {
-            while (a->next && a->next != action->data.srv_del.service) {
-                a = a->next;
-            }
-            if (a->next == action->data.srv_del.service) {
-                mdns_srv_item_t * b = a->next;
-                a->next = a->next->next;
-                _mdns_send_bye(&b, 1, false);
-                _mdns_remove_scheduled_service_packets(b->service);
-                _mdns_free_service(b->service);
-                free(b);
+        if (action->data.srv_del.service) {
+            if (_mdns_server->services == action->data.srv_del.service) {
+                _mdns_server->services = a->next;
+                _mdns_send_bye(&a, 1, false);
+                _mdns_remove_scheduled_service_packets(a->service);
+                _mdns_free_service(a->service);
+                free(a);
+            } else {
+                while (a->next && a->next != action->data.srv_del.service) {
+                    a = a->next;
+                }
+                if (a->next == action->data.srv_del.service) {
+                    mdns_srv_item_t * b = a->next;
+                    a->next = a->next->next;
+                    _mdns_send_bye(&b, 1, false);
+                    _mdns_remove_scheduled_service_packets(b->service);
+                    _mdns_free_service(b->service);
+                    free(b);
+                }
             }
         }