fix: NullPointerException on partitions revoked (#757)

[sangreal]

Description...
The race condition happens when there are partition revoked right after partition is assigned, and there are existing incompleteOffsets.

1. partition assigned and incompleteOffsets existed
2. right before begin to poll and process messages, it got revoked
3. the processingShard has no data yet
4. when revoked, try to delete entries with records from incompleteOffsets, no such record in entries

Checklist

• Documentation (if applicable)
• Changelog

[rkolesnev]

@sangreal - were you able to reproduce the issue? Could you add a test that reproduces it and tests for regression?

[rkolesnev]

/sem-approve

[rkolesnev]

/sem-approve

[sangreal]

@sangreal - were you able to reproduce the issue? Could you add a test that reproduces it and tests for regression?

@rkolesnev Thanks for the comment, I update the description and more details and UT is added.

[rkolesnev]

/sem-approve

[rkolesnev]

Hey @sangreal - thanks, can you please run license check / update license headers in updated / new files?
Refer to build output - https://confluentinc.semaphoreci.com/workflows/a37eff87-3a4f-493c-aa74-89d56d9a557a?pipeline_id=af6b4e93-5d9e-4e1e-9467-d0ee07c953ee.

[sangreal]

@rkolesnev thanks, I updated pr and please help trigger again.

[rkolesnev]

/sem-approve