Object reference not set to an instance of an object.
   at Microsoft.Xna.Framework.Graphics.OpenGLDevice.DeleteTexture(IGLTexture texture)
   at Microsoft.Xna.Framework.Graphics.OpenGLDevice.AddDisposeTexture(IGLTexture texture)
   at Microsoft.Xna.Framework.Graphics.Texture.Dispose(Boolean disposing)
   at Microsoft.Xna.Framework.Graphics.GraphicsResource.Dispose()
   at Microsoft.Xna.Framework.Graphics.GraphicsDevice.Dispose(Boolean disposing)
   at Microsoft.Xna.Framework.GraphicsDeviceManager.Dispose(Boolean disposing)
   at Microsoft.Xna.Framework.GraphicsDeviceManager.System.IDisposable.Dispose()
   at Microsoft.Xna.Framework.Game.Dispose(Boolean disposing)
   at Microsoft.Xna.Framework.Game.Dispose()
   at DungeonCrawler.Program.Main(String[] args)