All child classes of `MetaWaylandShellSurface` as well as
`MetaWaylandSurfaceRoleXWayland` should only sync their actor if
their toplevel surface has a window. Currently this check is done
in the actor-surface class, but not all surface classes have a
toplevel window, e.g. dnd-surfaces.
Move the check to the right places.
For subsurfaces this assumes that the subsurface is not the child of
a window-less surface (like, as stated above, e.g. a dnd-surface).
If we want to support subsurfaces of window-less surfaces in the future
we have to extend the check here.
But as this is not a regression, ignore this case for now.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/537
7e2a0ede16