[BUGFIX] Prevent type errors in ExportController

In case an export is created based on e.g.
an invalid preset, no PHP TypeError should
be occure.

This is now fixed by properly typecasting
the input data.

Additionally, two possible undefined array
key access warnings are fixed.

Resolves: #97403
Releases: main, 11.5
Change-Id: I994391909b44247879099ce92d61911c56ca7e39
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78723


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Jochen <rothjochen@gmail.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Benni Mack <benni@typo3.org>