[BUGFIX] PHP warning when importing a t3d without file storages

Added is_array() check before the foreach loop
running through the file storages.

Resolves: #72759
Releases: master
Change-Id: If78634e5474c0d86be529f4aa131a0d6a6f2f200
Reviewed-on: https://review.typo3.org/45987


Reviewed-by: Martin Kutschker <martin.kutschker@ymail.com>
Reviewed-by: Bernhard Kraft <kraftb@think-open.at>
Tested-by: Bernhard Kraft <kraftb@think-open.at>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>