[BUGFIX] Add fallback values for array keys in FormEngine

Array key undefined has been fixed by adding a fallback
value for array fields "doSaveFieldName" and
"elementBaseName"

Resolves: #94480
Releases: master
Change-Id: I89d315924136b527147f1b31fd0d7940719fcc6b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69716


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>