Ensure all handler events are covered

[AgeManning]

Issue Addressed

Logs indicated an RPC message was being dropped when the shutdown timer expired.

I couldn't see any obvious places where this could happen. The catch-all for this should be in the poll_close(). The only case I could think of would be events waiting to be processed in the handler.

This PR handles this edge case by ensuring all events are also handled before the handler is completely terminated.

As it stands, this should capture any currently in-flight messages and all events that are remaining to be processed.

[AgeManning]

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[jimmygchen]

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The pull request has been merged automatically at f69ccc3