br: fix region split failure due to empty split key

[SonglinLife]

What problem does this PR solve?

when tikv region has empty endKey, the br split region will failed due to empty key

Issue Number: close #56228

What changed and how does it work?

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.

None

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[ti-chi-bot]

Hi @SonglinLife. Thanks for your PR.

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[lance6716]

/ok-to-test

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 77.1034%. Comparing base (01797cb) to head (d5daab5).
Report is 41 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #56344        +/-   ##
================================================
+ Coverage   73.4215%   77.1034%   +3.6819%     
================================================
  Files          1619       1649        +30     
  Lines        446764     465996     +19232     
================================================
+ Hits         328021     359299     +31278     
+ Misses        98638      85184     -13454     
- Partials      20105      21513      +1408     

Flag	Coverage Δ
integration	53.6130% <0.0000%> (?)
unit	73.5271% <0.0000%> (+1.0211%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.9478% <ø> (ø)
parser	∅ <ø> (∅)
br	63.2242% <0.0000%> (+17.7014%)	⬆️

[lance6716]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lance6716, Leavrth

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• br/OWNERS [Leavrth]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-27 01:58:24.951243733 +0000 UTC m=+1790374.691667673: ☑️ agreed by lance6716.
• 2024-09-29 06:59:48.867384697 +0000 UTC m=+165344.287597710: ☑️ agreed by Leavrth.

[lance6716]

/check-issue-triage-complete

[lance6716]

/retest

[hawkingrei]

/ok-to-test

[lance6716]

/retest