producer.sendAsync is interrupted by client.close()

**Describe the bug**
If the client closes while sendAsync() is processed, the message is lost.

**To Reproduce**
see https://github.com/infiniticio/pulsar-bug-clientAsync

**Expected behavior**
The message should be sent before actually closing the client (https://apache-pulsar.slack.com/archives/C5Z4T36F7/p1629752614463900?thread_ts=1629723649.441700&cid=C5Z4T36F7)

**Additional context**
none

Start with the linked reproducer at infiniticio/pulsar-bug-clientAsync, then trace producer.sendAsync() and client.close() through the Java client. The fix is done when the reproduced message is sent before the client closes, without being lost.

Written by the indexing model from the issue text.