Created Issue: NullReferenceException when Hiding LayoutAnchorableItem [15495]

Hi Ado,

changing the VisibilityState (Hiding, Showing) of a LayoutAnchorableItem yields a NullReferenceException in LayoutAnchorableItem.OnVisibilityChanged(). (_anchorable is null, c.f. current MVVM Demo)

Cheers, mm