Fix CA2216

OpenRA.Platforms.Default/Sdl2GraphicsContext.cs

@@ -19,9 +19,10 @@ namespace OpenRA.Platforms.Default
 	sealed class Sdl2GraphicsContext : ThreadAffine, IGraphicsContext
 	{
 		readonly Sdl2PlatformWindow window;
-		bool disposed;
 		IntPtr context;
 
+		public string GLVersion => OpenGL.Version;
+
 		public Sdl2GraphicsContext(Sdl2PlatformWindow window)
 		{
 			this.window = window;
@@ -269,10 +270,12 @@ namespace OpenRA.Platforms.Default
 
 		public void Dispose()
 		{
-			if (disposed)
-				return;
+			Dispose(true);
+			GC.SuppressFinalize(this);
+		}
 
-			disposed = true;
+		void Dispose(bool _)
+		{
 			if (context != IntPtr.Zero)
 			{
 				SDL.SDL_GL_DeleteContext(context);
@@ -280,6 +283,9 @@ namespace OpenRA.Platforms.Default
 			}
 		}
 
-		public string GLVersion => OpenGL.Version;
+		~Sdl2GraphicsContext()
+		{
+			Dispose(false);
+		}
 	}
 }