statistics: fix the panic when to async load stats with dropped index

[hawkingrei]

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.

Project coverage is 73.8445%. Comparing base (e8f6026) to head (ccdb985).
Report is 3 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58887        +/-   ##
================================================
+ Coverage   73.1210%   73.8445%   +0.7235%     
================================================
  Files          1680       1710        +30     
  Lines        464549     472888      +8339     
================================================
+ Hits         339683     349202      +9519     
+ Misses       104015     102163      -1852     
- Partials      20851      21523       +672     

Flag	Coverage Δ
integration	45.9362% <0.0000%> (?)
unit	72.4008% <0.0000%> (+0.0828%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	45.4343% <ø> (+0.0266%)	⬆️

[hawkingrei]

/hold

wait for intergration test

[hawkingrei]

/unhold

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• pkg/statistics/OWNERS [AilinKid,winoros]

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-13 10:03:30.928762986 +0000 UTC m=+779954.217594691: ☑️ agreed by AilinKid.
• 2025-01-15 08:43:25.545139363 +0000 UTC m=+108077.000185510: ☑️ agreed by winoros.

[hawkingrei]

/retest

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #58957.

[hawkingrei]

/cherrypick release-8.5-20250114-v8.5.0

[ti-chi-bot]

@hawkingrei: new pull request created to branch release-8.5-20250114-v8.5.0: #58964.

In response to this:

/cherrypick release-8.5-20250114-v8.5.0

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