cpu high load with no exist group

consumer cause high cpu load。

### high load code：
```

consumer = PushConsumer(group) # rocketmq group is not exist
consumer.set_namesrv_addr(address)
consumer.subscribe(topic=topic, callback=callback)
consumer.start()

while True:
time.sleep(3600)

```

**this code run with no exception ， no warning hit。**

top monitor result here: