[BUGFIX] Always call GU::trimExplode with string in extbase/fluid

This avoids problem when GU::trimExplode is switched to native type
declarations.

Also fix some possible invalid array accesses.

Resolves: #97960
Relates: #97602
Releases: main
Change-Id: I6a08b7a20f12475fbee7a5a817f1618e9466087c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75210


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>