Merge pull request #2385 from cwensley/curtis/mac-fix-nre-with-scroll…

…able

Mac: Check for null Handler when resetting cursor rects in Scrollable

src/Eto.Mac/Forms/Controls/ScrollableHandler.cs

@@ -30,7 +30,7 @@ public ScrollableHandler Handler
 
 			public override void ResetCursorRects()
 			{
-				var cursor = Handler.Cursor;
+				var cursor = Handler?.Cursor;
 				if (cursor != null)
 					AddCursorRect(new CGRect(CGPoint.Empty, Frame.Size), cursor.ControlObject as NSCursor);
 			}