executor: fix retChk = nil in index_merge_reader (#46111)

[ti-chi-bot]

This is an automated cherry-pick of #46111

What problem does this PR solve?

Issue Number: close #46005

Problem Summary:

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.

None

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[codecov]

Codecov Report

Attention: Patch coverage is 84.21053% with 3 lines in your changes are missing coverage. Please review.

Please upload report for BASE (release-7.1@c585b3f). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.1     #46277   +/-   ##
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  Coverage               ?   77.3613%           
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  Files                  ?       1212           
  Lines                  ?     412671           
  Branches               ?          0           
================================================
  Hits                   ?     319248           
  Misses                 ?      76613           
  Partials               ?      16810           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Defined2014, wshwsh12

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• OWNERS [Defined2014,wshwsh12]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-05-31 05:16:09.551114871 +0000 UTC m=+3012723.308250436: ☑️ agreed by Defined2014.
• 2024-05-31 05:21:24.978683218 +0000 UTC m=+3013038.735818789: ☑️ agreed by wshwsh12.

[Defined2014]

/retest