[Revert] [iOS] CollectionView with grouped data crashes on iOS when the groups change - fix (#28246)

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

This reverts commit 47077b1.

* - add tests to make sure we validate regression

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;
 			}

src/Controls/tests/TestCases.Android.Tests/snapshots/android/BlankScreenOnNavigationBack.png

@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue28098"
+             xmlns:local="clr-namespace:Maui.Controls.Sample.Issues"
+             Title="Issue28098">
+    <ContentPage.BindingContext>
+        <local:MainPageViewModel x:Name="_viewModel"/>
+    </ContentPage.BindingContext>
+    <StackLayout Margin="20">
+        <Button Clicked="Button_Clicked"
+                AutomationId="Button"
+                Text="Button"/>
+        <CarouselView  WidthRequest="350"
+                       HeightRequest="570"
+                       HorizontalOptions="Fill"
+                       VerticalOptions="Fill"
+                       ItemsSource="{Binding Items}"
+                       Loop="False">
+            <CarouselView.ItemTemplate>
+                <DataTemplate>
+                    <StackLayout>
+                        <Image Source="dotnet_bot.png"
+                               WidthRequest="200"
+                               HeightRequest="200"
+                               Aspect="AspectFill"/>
+                        <Label Padding="10"
+                               VerticalOptions="Center"
+                               HorizontalOptions="Center"
+                               Text="{Binding Name}"/>
+                    </StackLayout>
+                </DataTemplate>
+            </CarouselView.ItemTemplate>
+        </CarouselView>
+
+    </StackLayout>
+</ContentPage>