[BUGFIX] Correctly append additionalTreelistUpdateFields

The list of additionalTreelistUpdateFields was not correctly
appended to the updateRequiringFields array.

Resolves: #37948
Releases: 6.2, 6.1, 6.0, 4.5
Change-Id: I7df514649203bf607a6ac3550c875c429e0f7328
Reviewed-on: https://review.typo3.org/25279
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind