Fix MQTT client io_desc slot leak on error/disconnect (5738)

Author: dgarske

src/port/stm32h563/mqtt_client.c

@@ -462,6 +462,14 @@ static int handle_disconnecting(void)
             ctx.socket_fd = -1;
         }
 
+        /* Release the wolfMQTT/wolfIP io_desc slot (in_use sentinel) so it is
+         * not leaked from the fixed MAX_WOLFMQTT_CTX pool. NULL it to avoid a
+         * double free if this path is re-entered. */
+        if (ctx.io_ctx) {
+            wolfMQTT_Cleanup_wolfIP(ctx.io_ctx);
+            ctx.io_ctx = NULL;
+        }
+
         ctx.state = MQTT_STATE_IDLE;
     }
 
@@ -513,6 +521,13 @@ int mqtt_client_poll(void)
                 wolfIP_sock_close(ctx.stack, ctx.socket_fd);
                 ctx.socket_fd = -1;
             }
+            /* Release the wolfMQTT/wolfIP io_desc slot (in_use sentinel) so it
+             * is not leaked from the fixed MAX_WOLFMQTT_CTX pool. NULL it to
+             * avoid a double free if this path is re-entered. */
+            if (ctx.io_ctx) {
+                wolfMQTT_Cleanup_wolfIP(ctx.io_ctx);
+                ctx.io_ctx = NULL;
+            }
             ctx.publish_pending = 0;
             ctx.state = MQTT_STATE_IDLE;
             break;