[ISSUE #1051 ] Close the channel before sending data if the consumer has been shutdown.

[cserwen]

What is the purpose of the change

Fix #1051

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[0daypwn]

https://github.com/apache/rocketmq-client-go/blob/da20ee7b0743a08ecf1fc53403f530b74eea2257/consumer/consumer.go#L296-L306 谁写入channel，谁负责关闭 是个好习惯

在已经有 close(pq.closeChan) 之后，再 close(pq.msgCh) 这个操作完全是多余的，关闭还会导致上述写入的风险。 在 close(pq.closeChan) 之后，只要不 close(pq.msgCh)， pq.putMessage 和 pq.getMessage 即使select到 msgCh 也不会有影响。 pq.putMessage 和 pq.getMessage 是msgCh唯二的使用者，之后是一定可以return的，也不存在会阻塞/泄露之类的问题。 因此我认为只去掉 close(pq.msgCh) 这部分即可 @cserwen

另外 consumer/consumer.go 这部分是基类 修改需要考虑 consumer/push_consumer.go consuemr/pull_consumer.go