Fix phantom beatmap sets appearing on carousel after delete/update

Regressed in c40c705.

As it turns out, `item.Item.Filtered.Value` is not the only condition
that should be checked to determine if a carousel item should be hidden
or not - `item.Item.State.Value != CarouselItemState.Collapsed` should
also be true. This was even available as the `item.Item.Visible`
convenience property, which is used in this commit.

Failing to check `item.Item.State.Value` led to setting non-zero alpha
on collapsed carousel items, leading to phantom beatmap sets appearing,
as the alpha was set in the entire carousel's `Update()` method, thus
firing every frame.

osu.Game/Screens/Select/BeatmapCarousel.cs

@@ -770,7 +770,7 @@ protected override void Update()
             {
                 updateItem(item);
 
-                if (!item.Item.Filtered.Value)
+                if (item.Item.Visible)
                 {
                     bool isSelected = item.Item.State.Value == CarouselItemState.Selected;