[BUGFIX] Loosen too strict checks for ModuleStateStorage

The replacement for fsMod comes with a bad
side-effect when using the topbar.

This change ensures that a "mount" can also be handed
in as "null" value.

Resolves: #94828
Related: #94762
Releases: master
Change-Id: I3e8c7ba7a83384297d8af52807be11e7e4115d59
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70463


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>