RenderTarget: Throw an error when disposing a bound target

Author: flibitijibibo

src/Graphics/RenderTarget2D.cs

@@ -180,6 +180,14 @@ protected override void Dispose(bool disposing)
 		{
 			if (!IsDisposed)
 			{
+				for (int i = 0; i < GraphicsDevice.renderTargetCount; i += 1)
+				{
+					if (GraphicsDevice.renderTargetBindings[i].RenderTarget == this)
+					{
+						throw new InvalidOperationException("Disposing target that is still bound");
+					}
+				}
+
 				IntPtr toDispose = Interlocked.Exchange(ref glColorBuffer, IntPtr.Zero);
 				if (toDispose != IntPtr.Zero)
 				{

src/Graphics/RenderTargetCube.cs

@@ -224,6 +224,14 @@ protected override void Dispose(bool disposing)
 		{
 			if (!IsDisposed)
 			{
+				for (int i = 0; i < GraphicsDevice.renderTargetCount; i += 1)
+				{
+					if (GraphicsDevice.renderTargetBindings[i].RenderTarget == this)
+					{
+						throw new InvalidOperationException("Disposing target that is still bound");
+					}
+				}
+
 				IntPtr toDispose = Interlocked.Exchange(ref glColorBuffer, IntPtr.Zero);
 				if (toDispose != IntPtr.Zero)
 				{