[BUGFIX] Prevent undefined array key in TimeTracker

Resolves: #98421
Releases: main, 11.5
Change-Id: I069ae69d4d396883393f76b1c9cf1b1cacaa0f9d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75852


Tested-by: core-ci <typo3@b13.com>
Tested-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>