[fix][client] Release semaphore before discarding messages in batchMessageContainer

[RobertIndie]

Fixes #17014

Motivation

The root cause of #17014 is a race condition in the batchMessageContainer when discarding the messages and releasing the semaphore. We need to release semaphore first and then discard messages. Otherwise, the user may observe that the semaphore has not been released after receiving the callback of that message.

Modifications

• Release semaphore before discarding messages in batchMessageContainer

Documentation

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