[BUGFIX] Invalid sys file storages must be ignored

If a storage is not available anymore, it must be ignored

Change-Id: Ie00af1bc086871c046ac4556c0119fc82d30a17e
Resolves: #55714
Releases: master, 6.2
Reviewed-on: http://review.typo3.org/41693


Reviewed-by: David Greiner <hallo@davidgreiner.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>