Fix some instances of null array key access

[mukeshpanchal27]

Trac ticket: https://core.trac.wordpress.org/ticket/63957

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[github-actions]

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[mukeshpanchal27]

Follow-up to #9849

[swissspidy]

How did you encounter these? #9845 doesn't report them, which would indicate a lack of test coverage.

[mukeshpanchal27]

How did you encounter these? #9845 doesn't report them, which would indicate a lack of test coverage.

Yes.

[swissspidy]

Yes there is a lack of test coverage?

In that case, some tests would be great :-)

[swissspidy]

Yes there is a lack of test coverage?

In that case, some tests would be great :-)

Curious to see any stack traces where these happen in action too, to find the root cause

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 60904
GitHub commit: de3741f

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.