We can end in `subsurface_committed()` in different scenarios
without the surface having an attached buffer. While setting
the mapped state to `true` in that case doesn't matter for
that (sub)surface itself, it triggers its own child subsurfaces
to get mapped when they shouldn't.
Closes https://gitlab.freedesktop.org/wayland/weston/-/issues/426
Signed-off-by: Robert Mader <robert.mader@collabora.com>
8b04534c76