[BUGFIX] EM: Uploading extensions fails with Fatal Errors

In case of an extension having dependencies, suggestions, or conflicts,
the Extension Manager fails with PHP Fatal Errors.

Change-Id: I26e8f12df7df7be3c21a6e7735635e38df70e87b
Resolves: #27836
Releases: 4.6, 4.5
Reviewed-on: http://review.typo3.org/6202
Reviewed-by: Stefan Neufeind
Tested-by: Xavier Perseguers
Reviewed-by: Xavier Perseguers
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter