clutter/actor: Show on all stage-views when actors have no allocation

When a badly behaving ClutterActor implementation manages to invalidate the allocation after the layout phase and before painting, we have no idea where the actor should be painted without running the whole layout machinery again.

For paint volumes in this case we pretend the actor covers the whole stage and queue full-stage redraws. When updating stage-views, we're also handling this case, but not in the most graceful way. Just like with paint volumes, we should assume an actor without a valid allocation is simply everywhere, so set priv->stage_views to all available stage views in that case.

Related: gnome-shell#6054 (moved)