event: never ignore changed frame extents

Changes to frame extents were only tracked if the frame was visible, but
we have to keep this information current even for invisible frames to
(not) render the correct area.

src/event.c

@@ -506,7 +506,7 @@ static inline void ev_property_notify(session_t *ps, xcb_property_notify_event_t
 	}
 
 	// If frame extents property changes
-	if (ps->o.frame_opacity > 0 && ev->atom == ps->atoms->a_NET_FRAME_EXTENTS) {
+	if (ev->atom == ps->atoms->a_NET_FRAME_EXTENTS) {
 		auto w = find_toplevel(ps, ev->window);
 		if (w) {
 			win_set_property_stale(w, ev->atom);