MediaPlayer: ActiveSongChanged
Fix comparison of null DisplayModes.
Merge pull request #1800 from flibitijibibo/mediaplayer-activesongchanged

MediaPlayer: ActiveSongChanged
Turns out we do not need the (object) cast.
Merge pull request #1801 from flibitijibibo/displaymode-comparison

Fix comparison of null DisplayModes.
Merge branch 'develop' of git://github.com/mono/MonoGame into monogame-sdl2

Also known as the most glorious no-op ever.