region: check if the query startkey and endkey specify an uncovered region

[JackL9u]

What problem does this PR solve?

when the query region [startKey, endKey] is an uncovered region, the function GetRegionCount now returns 0.

Issue Number: ref #6711

What is changed and how does it work?

Check List

Tests

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

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

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

Release note

None.

[ti-chi-bot]

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[ti-chi-bot]

Hi @JackL9u. Thanks for your PR.

I'm waiting for a tikv member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[rleungx]

/ok-to-test

[rleungx]

The tests failed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.02%. Comparing base (0402e15) to head (14f5455).
Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8743      +/-   ##
==========================================
- Coverage   70.10%   70.02%   -0.09%     
==========================================
  Files         517      517              
  Lines       79983    80029      +46     
==========================================
- Hits        56076    56038      -38     
- Misses      20339    20425      +86     
+ Partials     3568     3566       -2     

Flag	Coverage Δ
unittests	70.02% <100.00%> (-0.09%)	⬇️

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[okJiang]

Is this pr ready to review?