exeuctor: fix coprocessor goroutine leak for IndexMerge (#41610)

[ti-chi-bot]

This is an automated cherry-pick of #41610

What problem does this PR solve?

Issue Number: close #41605

Problem Summary: As issue said, for partialIndexWorker and partialTableWorker of IndexMerge, we may failed to call SelectResult.Close when got panic(oom) in IndexMerge.fetchHandles(). Therefore goroutines in coprocessor that tries to send copResp will stuck, because receiver already panic and copIterator.finishCh is never closed.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

exeuctor: fix coprocessor goroutine leak for IndexMerge

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• wshwsh12

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[XuHuaiyu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 32fd859