Handle user thrown exceptions in PartitionProcessor.

[conniey]

Description

Handles errors thrown from user code when PartitionProcessor.close or PartitionProcessor.processError is called. This ensures the clean-up method is called, and the partition can be claimed again.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
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Testing Guidelines

• Pull request includes test coverage for the included changes.

[azure-sdk]

API change check

API changes are not detected in this pull request.

[anuchandy]

thanks Connie!