[BUGFIX] Avoid calling string functions with non-strings in GU

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

Resolves: #97579
Relates: #97578
Releases: main, 11.5
Change-Id: I813075a74805b72781a493278e45aa1e9a1e2cc2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74573


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>