[BUGFIX] Fix notices in GraphicalFunctions

The provided width and height must be cast to a string to avoid
notices.

Resolves: #97911
Releases: main, 11.5
Change-Id: Ifa7428571026fbd0b0905729ea8ad699ab080bcb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75196


Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Oliver Bartsch <bo@cedev.de>