server: check visibility before sending global/global_remove

See the previous discussion at [1]: libwayland incorrectly skips
the visibility checks when sending global/global_remove events.
The check is only performed when a client performs a
wl_display.get_registry request.

[1]: https://gitlab.freedesktop.org/wayland/wayland/-/merge_requests/148



Signed-off-by: Simon Ser <contact@emersion.fr>