[BUGFIX] Add additional checks in Media Tools

Change-Id: I17343bd2bd64e047ee9dd977fac4f29b57104081
Releases: 3.1
Resolves: #61705
Reviewed-on: http://review.typo3.org/32858
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>