expression: resize the result for IfXXSig (#37417)

[ti-srebot]

cherry-pick #37417 to release-5.3
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/37428

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/37428:release-5.3-636d2728717e

---

What problem does this PR solve?

Issue Number: close #37414

Problem Summary:
The IfXXSig.fallbackEvalXX forgets to resize the result, thus trigger the index out of range error.

What is changed and how it works?

Check List

Tests

• Unit test

Side effects

N/A

Documentation

N/A

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• windtalker
• wshwsh12

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[ti-srebot]

/run-all-tests

[ti-srebot]

@XuHuaiyu you're already a collaborator in bot's repo.

[sre-bot]

Code Coverage Details: https://codecov.io/github/pingcap/tidb/commit/5f9505382cd2255004629af8cad1ce5d5ceee932

[windtalker]

LGTM

[XuHuaiyu]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 5f95053

[ti-chi-bot]

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