Better error for Texture2D.FromStream when graphics device is null.

[Beng89]

I was recently working on loading textures with Texture2D.FromStream and kept getting the following error:

"This image format is not supported"

After fighting with this for about 30 minutes, I realized that the GraphicsDevice I was passing to the method as an argument was unintentionally null. The error that I received above was less than helpful when debugging this problem. Perhaps a better error could be throw when a null GraphicsDevice is provided (such as a NullReferenceException or an ArgumentException).