planner: fix the possible panic when fixcontrol#44855 enabled

[winoros]

What problem does this PR solve?

Issue Number: close #59762

Problem Summary:

What changed and how does it work?

when we fixed the IdxCols for the path, we didn't update the full one for it.
So the full one may be smaller than the prefix one.

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.

fix the issue that the TiDB may panic when fixcontrol#44855 is enabled
修复当 fixcontrol#44855 开启时，TiDB 的会话可能执行崩溃的问题

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.3633%. Comparing base (fed0251) to head (d698405).
Report is 765 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #59763        +/-   ##
================================================
+ Coverage   72.9574%   73.3633%   +0.4058%     
================================================
  Files          1697       1698         +1     
  Lines        468964     469345       +381     
================================================
+ Hits         342144     344327      +2183     
+ Misses       105748     103940      -1808     
- Partials      21072      21078         +6     

Flag	Coverage Δ
integration	42.7776% <100.0000%> (?)
unit	72.4514% <100.0000%> (+0.0009%)	⬆️

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Components	Coverage Δ
dumpling	∅ <ø> (∅)
parser	∅ <ø> (∅)
br	46.4784% <ø> (+0.0360%)	⬆️

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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Needs approval from an approver in each of these files:

• OWNERS [AilinKid,hawkingrei]
• pkg/planner/OWNERS [AilinKid,hawkingrei]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-02-26 02:25:37.255942875 +0000 UTC m=+409085.209101142: ☑️ agreed by AilinKid.
• 2025-02-26 02:31:21.753999243 +0000 UTC m=+409429.707157509: ☑️ agreed by hawkingrei.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #60444.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #62310.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #62311.
But this PR has conflicts, please resolve them!

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #62312.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #62313.