[net7.0] _itemsSource may be null in CarouselViewLoopManager (#11967)

* _itemsSource may be null

I'm seeing a NullReferenceException in this method. There are no guards against `_itemsSource` being null, so dereferencing it to get its `Count` seems likely to be the problem.

* fix dropped semicolon

Co-authored-by: Nicholas Bauer <nicholasbauer@outlook.com>

src/Controls/src/Core/Handlers/Items/Android/CarouselViewLoopManager.cs

@@ -14,6 +14,8 @@ public void CenterIfNeeded(RecyclerView recyclerView, bool isHorizontal)
 		{
 			if (!(recyclerView.GetLayoutManager() is LinearLayoutManager linearLayoutManager))
 				return;
+			if (_itemsSource is null)
+				return;
 
 			var itemSourceCount = _itemsSource.Count;
 
@@ -43,7 +45,9 @@ public int GetGoToIndex(RecyclerView recyclerView, int carouselPosition, int new
 		{
 			if (!(recyclerView.GetLayoutManager() is LinearLayoutManager linearLayoutManager))
 				return -1;
-
+			if (_itemsSource is null)
+				return -1;
+
 			var currentCarouselPosition = carouselPosition;
 			var itemSourceCount = _itemsSource.Count;