fullscreen-shell: Test for device presence properly

We should be testing device counts, not pointers.  The pointers are
persistent state that never gets freed, and are an inaccurate indicator
of device presence after the last release.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>

fullscreen-shell/fullscreen-shell.c

@@ -102,7 +102,7 @@ seat_caps_changed(struct wl_listener *l, void *data)
 	listener = container_of(l, struct pointer_focus_listener, seat_caps);
 
 	/* no pointer */
-	if (seat->pointer) {
+	if (seat->pointer_device_count) {
 		if (!listener->pointer_focus.link.prev) {
 			wl_signal_add(&seat->pointer->focus_signal,
 				      &listener->pointer_focus);
@@ -113,7 +113,7 @@ seat_caps_changed(struct wl_listener *l, void *data)
 		}
 	}
 
-	if (seat->keyboard && seat->keyboard->focus != NULL) {
+	if (seat->keyboard_device_count && seat->keyboard->focus != NULL) {
 		wl_list_for_each(fsout, &listener->shell->output_list, link) {
 			if (fsout->surface) {
 				weston_surface_activate(fsout->surface, seat);