release-24.3: crosscluster/logical: avoid panic in multi-table streams involving UDTs

[dt]

Backport 1/1 commits from #141634.

/cc @cockroachdb/release

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Previously a single LDR stream involving multiple tables would fail to be created if the tables used user-defined types due to a bug in the helper used to resolve UDTs when called in a loop where successfully resolving a type returned a nil map that was then passed to the next call in the loop, causing it to panic.

Release note (bug fix): fix a bug that prevented starting multi-table LDR streams on tables that used user-defined types.
Epic: none.

Fixes #141598.

Release justification: bug fix.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
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If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
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Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is