[BUGFIX] Always call GU::intExplode with a string in EXT:core

This helps avoid breakage when GeneralUtility will switch to
strict mode.

This change also prevents a whole bunch of possible invalid
array access warnings.

Resolves: #97582
Relates: #97580
Releases: main
Change-Id: I950d64fcb2f16b5044eeff465c85b4022525ceb6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74863


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