sink: ignore the empty row event (#3144)

[ti-chi-bot]

This is an automated cherry-pick of #3144

What problem does this PR solve?

close https://github.com/pingcap/ticdc/issues/2612.

What is changed and how it works?

ignore the empty row event.

Check List

Tests

• Unit test (TBD)

Code changes

None

Side effects

None

Related changes

• Need to cherry-pick to the release branch

Release note

None

[ti-chi-bot]

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[overvenus]

/merge

[ti-chi-bot]

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

Commit hash: cbfd0cb