Make FMVPlayer in TD use a completely black background

Fixes #6211.
Make FMVPlayer in RA use a completely black background
Merge pull request #6220 from obrakmann/fix6211

Make background of FMVPlayers in TD and RA black
avoid NullReferenceException in updatedRegion

fixes #6166
Merge pull request #6226 from Mailaender/shroud-updatedregion-nre

Fixed a crash when there are no actors to reveal shroud on the map.