owner,scheduler(cdc): fix nil pointer panic in owner scheduler (#2980) (#4007)

[ti-chi-bot]

This is an automated cherry-pick of #4007

What problem does this PR solve?

close #2980

What is changed and how it works?

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

Fix nil pointer panic encountered when scheduler cleanup finished operations 

[ti-chi-bot]

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[CharlesCheung96]

/run-kafka-tests
/run-integration-tests

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (release-5.1@a71a5a9). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff                @@
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[CharlesCheung96]

@nongfushanquan

[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: e5234ff