Fix the operation of unregistering listener

- Add check for empty listener list in find_listener_entry function.
- Reset notification queue when all listeners are removed.
- Change queue operation to send remove_listener message to the front of the queue.

Refs #1085, #1096 and fixes #1102

src/relay_chn_notify.c

@@ -118,6 +118,11 @@ void relay_chn_notify_deinit(void)
  */
 static relay_chn_listener_entry_t* find_listener_entry(relay_chn_state_listener_t listener)
 {
+    if (listLIST_IS_EMPTY(&listeners)) {
+        ESP_LOGD(TAG, "No listeners registered");
+        return NULL;
+    }
+
     // Iterate through the linked list of listeners
     for (ListItem_t *pxListItem = listGET_HEAD_ENTRY(&listeners);
          pxListItem != listGET_END_MARKER(&listeners);
@@ -164,6 +169,11 @@ static void do_remove_listener(relay_chn_state_listener_t listener)
     } else {
         ESP_LOGD(TAG, "Listener %p not found for unregistration.", listener);
     }
+
+    if (listLIST_IS_EMPTY(&listeners)) {
+        // Flush all pending notifications in the queue
+        xQueueReset(notify_msg_queue);
+    }
 }
 
 esp_err_t relay_chn_notify_add_listener(relay_chn_state_listener_t listener)
@@ -191,7 +201,7 @@ void relay_chn_notify_remove_listener(relay_chn_state_listener_t listener)
     }
 
     relay_chn_notify_msg_t msg = { .cmd = RELAY_CHN_NOTIFY_CMD_REMOVE_LISTENER, .payload.listener = listener };
-    if (xQueueSend(notify_msg_queue, &msg, 0) != pdTRUE) {
+    if (xQueueSendToFront(notify_msg_queue, &msg, 0) != pdTRUE) {
         ESP_LOGW(TAG, "Notify queue is full, failed to queue remove_listener");
     }
 }