fullscreen-shell: fix black output

Fullscreen-shell forgot to mark the weston_surface as mapped when
mapping the surface and view. With
f962b48958 that means no surface from
fullscreen-shell clients is eveer shown. Most notably this broke
screen-share plugin, which is maybe the only "real" user of
fullscreen-shell.

Fix this oversight. Now screen-share works again with RDP-backend.

Fixes: f962b48958
	"compositor: Only create paint nodes for mapped surfaces/views"
	(currently unreleased)

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

fullscreen-shell/fullscreen-shell.c

@@ -625,6 +625,7 @@ fs_output_apply_pending(struct fs_output *fsout)
 			return;
 		}
 		fsout->view->is_mapped = true;
+		fsout->surface->is_mapped = true;
 
 		wl_signal_add(&fsout->surface->destroy_signal,
 			      &fsout->surface_destroyed);