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

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

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

Resolves: #97584
Related: #97578
Releases: main
Change-Id: Iaf23147d2ffdbca3a5c8205b2c32926c46084021
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75079


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>