[Fix] Fix the cdc bug about NPE when the original table deletes a field

[JohnZp]

Purpose of this pull request

Fix NPE, it introduced by #5575

Does this PR introduce any user-facing change?

No

How was this patch tested?

Nothing

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If you are contributing the connector code, please check that the following files are updated:
  1. Update change log that in connector document. For more details you can refer to connector-v2
  2. Update plugin-mapping.properties and add new connector information in it
  3. Update the pom file of seatunnel-dist
• Update the release-note.

[Hisoka-X]

Could you open your fork repository action follow the guide?

[JohnZp]

@Hisoka-X The checked have passed, please help review

[Hisoka-X]

Make sense to me, cc @hailin0 @ic4y .

[liugddx]

Good job.