[Bug] PushConsumer may cause consumption duplication in some scenarios due to concurrency issues. #479

BUG REPORT

1. Please describe the issue you observed:

• What did you do (The steps to reproduce)?

1. Start a consumer client c1.
2. Start another consumer client c2 and immediately shut it down.
3. Observe the consumption duplication of the consumer client c1.
   

• What did you expect to see?
  There's no consumption duplication.
• What did you see instead?
  The consumer client c1 duplicate consume the same message many times at the same timestamp.

4. Please tell us about your environment:

• What is your OS?
  Ubuntu & CentOS
• What is your client version?
  latest
• What is your RocketMQ version?
  5.9

4. Other information (e.g. detailed explanation, logs, related issues, suggestions on how to fix, etc):