Fixes #3425. v1 - ScrollView is not clearing the background by duplicating views.

Terminal.Gui/Views/ScrollView.cs

@@ -349,7 +349,7 @@ namespace Terminal.Gui {
 		{
 			Driver.SetAttribute (GetNormalColor ());
 			SetViewsNeedsDisplay ();
-			//Clear ();
+			Clear ();
 
 			var savedClip = ClipToBounds ();
 			OnDrawContent (new Rect (ContentOffset,