expression: fix substring_index crash tiflash in some case (#9137)

[ti-chi-bot]

This is an automated cherry-pick of #9137

What problem does this PR solve?

Issue Number: close #9116

Problem Summary:

What is changed and how it works?

Fix tiflash crash caused by function `substring_index` in some corner cases

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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

Fix tiflash crash caused by function `substring_index` in some corner cases

[windtalker]

LGTM

[ti-chi-bot]

@windtalker: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

LGTM

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[ti-chi-bot]

@solotzg: adding LGTM is restricted to approvers and reviewers in OWNERS files.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: solotzg, windtalker

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[wshwsh12]

/run-all-tests

[wshwsh12]

/run-all-tests

[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

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