planner: fix the panic when we calculate the partition range (#23651)

[ti-srebot]

cherry-pick #23651 to release-4.0
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# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/23689

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---

What problem does this PR solve?

Issue Number: close #23622

Problem Summary: When we simplify the partition range, we do not consider the length of the slice. So it will cause panic in some cases.

What is changed and how it works?

Check the length before the simplify first. If the length of the slice is zero, we should return early.

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Side effects

• Performance regression
  • Consumes more CPU
  • Consumes more MEM
• Breaking backward compatibility

Release note

• fix the panic when we calculate the partition range

[ti-srebot]

/run-all-tests

[ti-srebot]

No release note, Please follow https://github.com/pingcap/community/blob/master/contributors/release-note-checker.md

[ti-srebot]

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

[qw4990]

/merge

[ti-chi-bot]

@qw4990: /merge in this pull request requires 2 /lgtm.

In response to this:

/merge

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[qw4990]

/merge

[ti-chi-bot]

@qw4990: /merge in this pull request requires 2 /lgtm.

In response to this:

/merge

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[XuHuaiyu]

/lgtm

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• XuHuaiyu
• qw4990

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[qw4990]

/merge

[ti-chi-bot]

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

Commit hash: 23bd64e

[qw4990]

/merge

[qw4990]

/merge

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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