[BUGFIX] Only show preview of non-hidden images

Don't show preview of hidden images in backend e.g.
page module.

Change-Id: I11fbfdbdf9767066dbb3380b543d79c239e6c4a2
Resolves: #73481
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/46735


Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>