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 https://github.com/pingcap/tiflash/issues/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

• [x] 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

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

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

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tiflash/blob/release-8.1/OWNERS)~~ [solotzg,windtalker] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-06-11 10:04:03.237567634 +0000 UTC m=+458997.290879548: :ballot_box_with_check: agreed by windtalker.
• 2024-06-12 04:46:48.048494807 +0000 UTC m=+526362.101806731: :ballot_box_with_check: agreed by solotzg.

[wshwsh12]

/run-all-tests