fix: mqtt默认值

xymanager_framework/src/main/java/com/shxy/xymanager_framework/config/MqttConfig.java

@@ -38,11 +38,10 @@ public class MqttConfig {
 
     @Bean
     public MqttClient mqttClient(MqttConnectOptions options) throws MqttException {
-        if (!enable) {
-            return null;
-        }
         MqttClient client = new MqttClient(broker, clientId);
+        if (enable) {
             client.connect(options);
+        }
         return client;
     }
 }