[BUGFIX] Allow processed folders in different storage

The processingfolder of a storage can now be a combined identifier.
This makes it possible to have the processed files outside of the
storage in case of a read-only storage for instance.

Releases: master, 6.2
Resolves: #61463
Change-Id: I4f0e187db2aede33be40f62df3bb9f63e9706d46
Reviewed-on: http://review.typo3.org/32921


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>