[BUGFIX] Fix uninitialized string offset in TypoScriptParser

Resolves: #97465
Releases: main, 11.5
Change-Id: Iae6db28b4af2dcdbc1826f14fd0967415a81a341
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74398


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>