statistics: fix the panic when to async load stats with dropped index (#58887)

[ti-chi-bot]

This is an automated cherry-pick of #58887

What problem does this PR solve?

Issue Number: close #58865

Problem Summary:

What changed and how does it work?

when drop index happen during the async load. it will happen the panic.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

with 1m tables's DDL and DML, this problem will not happen again.

• 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

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5@920eb53). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #58957   +/-   ##
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  Coverage               ?   56.9209%           
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  Files                  ?       1770           
  Lines                  ?     627463           
  Branches               ?          0           
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  Hits                   ?     357158           
  Misses                 ?     246194           
  Partials               ?      24111           

Flag	Coverage Δ
integration	36.7718% <0.0000%> (?)
unit	72.6288% <0.0000%> (?)

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

Components	Coverage Δ
dumpling	52.8711% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	52.2998% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hawkingrei, winoros

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• pkg/statistics/OWNERS [hawkingrei,winoros]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-15 16:28:38.04538621 +0000 UTC m=+135989.500432354: ☑️ agreed by hawkingrei.
• 2025-01-15 16:28:54.775907072 +0000 UTC m=+136006.230953221: ☑️ agreed by winoros.