cdc: before drain the capture, check the capture can be found

[3AceShowHand]

What problem does this PR solve?

What is changed and how it works?

Check List

Tests

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

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

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

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release notes:

NONE

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• nexustar

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[codecov-commenter]

Codecov Report

Base: 57.16% // Head: 57.00% // Decreases project coverage by -0.16% ⚠️

Coverage data is based on head (76cc7db) compared to base (fb0be5e).
Patch coverage: 54.55% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2059      +/-   ##
==========================================
- Coverage   57.16%   57.00%   -0.16%     
==========================================
  Files         313      313              
  Lines       33492    33512      +20     
==========================================
- Hits        19143    19101      -42     
- Misses      12106    12163      +57     
- Partials     2243     2248       +5     

Flag	Coverage Δ
cluster	45.74% <54.55%> (-0.17%)	⬇️
dm	26.18% <0.00%> (-0.07%)	⬇️
playground	14.94% <0.00%> (-0.02%)	⬇️
tiup	16.15% <0.00%> (-0.04%)	⬇️
unittest	22.59% <0.00%> (-0.02%)	⬇️

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

Impacted Files	Coverage Δ
pkg/cluster/spec/cdc.go	56.32% <0.00%> (-0.90%)	⬇️
pkg/cluster/api/cdcapi.go	44.19% <60.00%> (-11.94%)	⬇️
pkg/cluster/spec/pump.go	61.94% <0.00%> (-4.52%)	⬇️
pkg/repository/store/txn.go	56.91% <0.00%> (-2.13%)	⬇️
pkg/cluster/api/dmapi.go	59.88% <0.00%> (-1.74%)	⬇️
pkg/cluster/api/pdapi.go	52.04% <0.00%> (-1.41%)	⬇️
pkg/cluster/spec/tiflash.go	69.31% <0.00%> (-0.66%)	⬇️
pkg/cluster/operation/destroy.go	59.66% <0.00%> (-0.64%)	⬇️
... and 2 more

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[nexustar]

/merge

[ti-chi-bot]

@nexustar: /merge in this pull request requires 1 approval(s).

In response to this:

/merge

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[nexustar]

/merge

[ti-chi-bot]

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

Commit hash: 76cc7db