Revert "CollectionView with grouped data crashes on iOS when the groups change - fix (#27991)"

This reverts commit 47077b1.

Author: PureWeen

src/Controls/src/Core/Handlers/Items/iOS/ObservableGroupedSource.cs

@@ -315,11 +315,6 @@ void Move(NotifyCollectionChangedEventArgs args)
 
 		int GetGroupCount(int groupIndex)
 		{
-			if (groupIndex < 0 || groupIndex >= _groupSource.Count)
-			{
-				return 0;
-			}
-
 			switch (_groupSource[groupIndex])
 			{
 				case IList list:
@@ -339,11 +334,6 @@ int GetGroupCount(int groupIndex)
 
 		object GetGroupItemAt(int groupIndex, int index)
 		{
-			if (groupIndex < 0 || groupIndex >= _groupSource.Count)
-			{
-				return -1;
-			}
-
 			switch (_groupSource[groupIndex])
 			{
 				case IList list:

src/Controls/src/Core/Handlers/Items/iOS/ObservableItemsSource.cs

@@ -314,7 +314,7 @@ void Update(Action<UICollectionView> update, NotifyCollectionChangedEventArgs ar
 				return;
 
 			var collectionView = controller.CollectionView;
-			if (collectionView.Hidden || collectionView.Window == null)
+			if (collectionView.Hidden)
 			{
 				return;
 			}