Cache status line position to reduce option lookups during output.

cmd-set-option.c

@@ -248,6 +248,8 @@ cmd_set_option_exec(struct cmd *self, struct cmdq_item *item)
 		RB_FOREACH(w, windows, &windows)
 			layout_fix_panes(w, w->sx, w->sy);
 	}
+	RB_FOREACH (s, sessions, &sessions)
+		status_update_saved(s);
 
 	/*
 	 * Update sizes and redraw. May not always be necessary but do it