waylandsink/wlwindow: do not commit a resize when it happens due to a video info...

waylandsink/wlwindow: do not commit a resize when it happens due to a video info change

1) We know that gst_wayland_sink_render() will commit the surface
   in the same thread a little later, as gst_wl_window_set_video_info()
   is always called from there, so we can save the compositor from
   some extra calculations.
2) We should not commit a resize with the new video info while we are still
   showing the buffer of the previous video, with the old caps, as that
   would probably be a visible resize glitch.