Tighten select-all helper semantics

ErsatzTV/Pages/MediaCardSelectionHelper.cs

@@ -10,11 +10,15 @@ public static class MediaCardSelectionHelper
         ISet<MediaCardViewModel> selectedItems,
         IEnumerable<MediaCardViewModel> cards)
     {
-        List<MediaCardViewModel> cardList = (cards ?? Enumerable.Empty<MediaCardViewModel>()).ToList();
-
         selectedItems.Clear();
-        selectedItems.UnionWith(cardList);
 
-        return cardList.LastOrDefault();
+        MediaCardViewModel last = default;
+        foreach (MediaCardViewModel card in cards ?? Enumerable.Empty<MediaCardViewModel>())
+        {
+            last = card;
+            selectedItems.Add(card);
+        }
+
+        return last;
     }
 }

ErsatzTV/Pages/MultiSelectBase.cs

@@ -44,8 +44,6 @@ public class MultiSelectBase<T> : FragmentNavigationBase
     {
         MediaCardViewModel lastSelected = MediaCardSelectionHelper.SelectAllPageItems(SelectedItems, cards);
         _recentlySelected = Optional(lastSelected);
-
-        StateHasChanged();
     }
 
     protected void ClearSelection()