修复bug：rts-sim-testing-client的#2issue: joylink/rts-sim-testing-client#2 (comment)

src/message/MqttBroker.ts

@@ -85,12 +85,14 @@ export class MqttMsgClient extends MessageClient {
   }
   unsubscribe0(destination: string): void {
     console.debug('MQTT取消订阅执行', destination);
+    // 删除指定订阅的消息处理器
+    this.subMsgHandler.delete(destination);
+    // 通知服务器取消订阅
     this.cli.unsubscribe(destination, (error, packet) => {
       if (error) {
         console.warn('MQTT 取消订阅失败', error);
       } else {
         console.debug('MQTT 取消订阅成功', packet);
-        this.subMsgHandler.delete(destination);
       }
     });
   }