Regressed in c40c70509e.
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.
7b274083d3