fix for issue #2000 button with rendertransform don't fire click

src/Avalonia.Controls/Button.cs

@@ -251,7 +251,9 @@ namespace Avalonia.Controls
                 IsPressed = false;
                 e.Handled = true;
 
-                if (ClickMode == ClickMode.Release && new Rect(Bounds.Size).Contains(e.GetPosition(this)))
+                //only renderer (hittesting) know better whether pointer is over the bounds of the button
+                if (ClickMode == ClickMode.Release && 
+                    (IsPointerOver || new Rect(Bounds.Size).Contains(e.GetPosition(this))))
                 {
                     OnClick();
                 }