Hack around problem with Item 0 being shown...

...when switching to a scrolled UniformGridLayout.

src/Avalonia.Layout/UniformGridLayoutState.cs

@@ -71,6 +71,13 @@ namespace Avalonia.Layout
                     }
 
                     _cachedFirstElement.Measure(availableSize);
+
+                    // This doesn't need to be done in the UWP version and I'm not sure why. If we
+                    // don't do this here, and we receive a recycled element then it will be shown
+                    // at its previous arrange point, but we don't want it shown at all until its
+                    // arranged.
+                    _cachedFirstElement.Arrange(new Rect(-10000.0, -10000.0, 0, 0));
+
                     SetSize(_cachedFirstElement, layoutItemWidth, LayoutItemHeight, availableSize, stretch, orientation, minRowSpacing, minColumnSpacing);
 
                     // See if we can move ownership to the flow algorithm. If we can, we do not need a local cache.