[BUGFIX] Allow reading files if storage is not browsable

Whether a storage is browsable or not should not
affect the possibility to read a file with a
given identifier.

Releases: 6.0, 6.1, 6.2
Resolves: #51010

Change-Id: Ic754143ed39a277f14c488c5b0d4c050dde027df
Reviewed-on: https://review.typo3.org/23065
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel