*: check if GetStore returns nil (#4347)

[ti-chi-bot]

This is an automated cherry-pick of #4347

close #4344

Signed-off-by: disksing i@disksing.com

What problem does this PR solve?

If we use remove tombstone, GetStore may return nil. We should check it.

What is changed and how it works?

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

Fix panic issue after TiKV node scales in

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• nolouch
• rleungx

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[codecov]

Codecov Report

Merging #4379 (a982d15) into release-5.0 (a4a4c5a) will increase coverage by 0.01%.
The diff coverage is 33.33%.

@@               Coverage Diff               @@
##           release-5.0    #4379      +/-   ##
===============================================
+ Coverage        74.87%   74.88%   +0.01%     
===============================================
  Files              245      245              
  Lines            24336    24348      +12     
===============================================
+ Hits             18221    18233      +12     
+ Misses            4504     4501       -3     
- Partials          1611     1614       +3     

Flag	Coverage Δ
unittests	74.88% <33.33%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
server/schedule/region_scatterer.go	86.09% <0.00%> (-2.39%)	⬇️
server/schedule/checker/replica_strategy.go	88.37% <50.00%> (-4.13%)	⬇️
server/schedulers/shuffle_region.go	75.67% <50.00%> (-1.79%)	⬇️
server/statistics/store.go	90.67% <100.00%> (ø)
server/id/id.go	76.19% <0.00%> (-4.77%)	⬇️
server/election/leadership.go	85.88% <0.00%> (-1.18%)	⬇️
client/client.go	72.10% <0.00%> (-0.14%)	⬇️
server/server.go	72.43% <0.00%> (ø)
server/grpc_service.go	47.39% <0.00%> (+0.22%)	⬆️
client/base_client.go	82.98% <0.00%> (+0.51%)	⬆️
... and 4 more

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[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Please provide the associated issue number in the commit messages, for example: close #12345, or ref #12345.

[nolouch]

/merge

[ti-chi-bot]

@nolouch: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

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

Commit hash: a982d15

[nolouch]

/rebuild