executor: fix query panic on INFORMATION_SCHEMA.CLUSTER_SLOW_QUERY with some slow query files (#54325)

[ti-chi-bot]

This is an automated cherry-pick of #54325

What problem does this PR solve?

Issue Number: close #54324

Problem Summary:

What changed and how does it work?

The old code does not handle all the cases well.
if i >= len(lines)-1 should be a typo, it should be something like if i >= len(chars)-1
And the simplified logic is just the same as this PR.

Check List

Tests

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

  • I checked and no code files have been changed.

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #54935   +/-   ##
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  Coverage               ?   74.0944%           
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  Files                  ?       1096           
  Lines                  ?     355685           
  Branches               ?          0           
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  Hits                   ?     263543           
  Misses                 ?      75455           
  Partials               ?      16687           

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-26 07:45:33.798869094 +0000 UTC m=+1203955.789810563: ☑️ agreed by Defined2014.
• 2024-08-26 13:31:20.987516681 +0000 UTC m=+790676.121966803: ☑️ agreed by tiancaiamao.