[BUGFIX] Properly check instance of folder parameter

This will prevent type errors in case
given folder parameter is set but not
a Folder object.

Resolves: #102016
Related: #102014
Releases: main, 12.4
Change-Id: I828cab2ab1a5a649ba6fdf08375453b4c3382432
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81179


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Jochen Roth <rothjochen@gmail.com>
Tested-by: Jochen Roth <rothjochen@gmail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>