[BUGFIX] Do not hand invalid input to ResourceFactory

A phpstan related patch revealed a flaw in EXT:form
PropertyMappingConfiguration when an "EXT:" path was
passed to the FAL ResourceFactory.

Instead of relying on the InvalidArgumentException
this patch now prevents the invalid argument from being
passed in the first place.

Resolves: #92908
Related: #92264
Releases: master, 10.4
Change-Id: I09ff5e28c28e8bbc2de954c1b9077969befb3646
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/66852


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Benni Mack <benni@typo3.org>