[UWP] Fix issue where if ItemsSouce is initially null, listview would never render (#2976)

Xamarin.Forms.Platform.UAP/ListViewRenderer.cs

@@ -171,7 +171,7 @@ namespace Xamarin.Forms.Platform.UWP
 			else if (e.PropertyName == ListView.ItemsSourceProperty.PropertyName)
 			{
 				ClearSizeEstimate();
-				((CollectionViewSource)List.DataContext).Source = Element.ItemsSource;
+				ReloadData();
 			}
 			else if (e.PropertyName == Specifics.SelectionModeProperty.PropertyName)
 			{