planner: fix the possible panic when fixcontrol#44855 enabled (#59763)

[ti-chi-bot]

This is an automated cherry-pick of #59763

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

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	7260a9a	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev	7260a9a	link	true	/test check-dev
idc-jenkins-ci-tidb/build	7260a9a	link	true	/test build

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