[BUGFIX] Force correct type in FormViewHelper

Add several type casts to avoid notices.

Resolves: #101486
Releases: main, 12.4, 11.5
Signed-off-by: Torben Hansen <derhansen@gmail.com>
Change-Id: I87f02e129d91ae9902ad74f306f11915d12037b0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80246


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>