set `c->prev` in setmon() and not in mapnotify()

dwl.c

@@ -1424,7 +1424,6 @@ mapnotify(struct wl_listener *listener, void *data)
 	client_get_geometry(c, &c->geom);
 	c->geom.width += 2 * c->bw;
 	c->geom.height += 2 * c->bw;
-	c->prev = c->geom;
 
 	/* Insert this client into client lists. */
 	wl_list_insert(&clients, &c->link);
@@ -1960,6 +1959,7 @@ setmon(Client *c, Monitor *m, unsigned int newtags)
 	if (oldmon == m)
 		return;
 	c->mon = m;
+	c->prev = c->geom;
 
 	/* TODO leave/enter is not optimal but works */
 	if (oldmon) {