executor: fix retChk = nil in index_merge_reader

[Defined2014]

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

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None

[tiprow]

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[codecov]

Codecov Report

Merging #46111 (2b2e181) into master (3846e80) will decrease coverage by 1.4827%.
Report is 49 commits behind head on master.
The diff coverage is 85.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #46111        +/-   ##
================================================
- Coverage   74.7667%   73.2841%   -1.4827%     
================================================
  Files          1292       1306        +14     
  Lines        398141     405418      +7277     
================================================
- Hits         297677     297107       -570     
- Misses        81100      89853      +8753     
+ Partials      19364      18458       -906     

Flag	Coverage Δ
integration	25.8428% <15.0000%> (-20.4201%)	⬇️
unit	73.9643% <85.0000%> (+0.6122%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.2114% <ø> (+0.1457%)	⬆️
br	48.0463% <ø> (-16.4662%)	⬇️

[XuHuaiyu]

i -> chunkRowOffset ?

[Defined2014]

Done.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-08-16 08:33:14.987942708 +0000 UTC m=+706359.536958695: ☑️ agreed by wshwsh12.
• 2023-08-21 06:03:01.126316531 +0000 UTC m=+1129345.675332502: ☑️ agreed by XuHuaiyu.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #46277.