Fixes attempt to dispose a RenderTarget2D on a GraphicsDevice, that is null.  This can cause the Graphics drawing routines to stop drawing, while the game play continues, and spam of NullReferenceExceptions being thrown.
Ugly hack to work around Failure to get VolumeObject on Windows 7 platforms.  I believe this issue comes from computers that have more then 1 Sound device on it, but no idea how to properly fix this, without having to hack in a goto to resolve the issue.  If it doesn't get the Volume Object within 5 tries (Which equals 6 actual attempts to get the device), it will fail.
Merge branch 'develop' of http://github.com/eumario/MonoGame into pr2980

Conflicts:
	MonoGame.Framework/Graphics/RenderTarget2D.OpenGL.cs