设置Discuz 7论坛游客可以查看图片，但不能下载附件.

viewthread.php找到：

1. $allowgetattach = !empty($forum['allowgetattach']) || ($allowgetattach && !$forum['getattachperm']) || forumperm($forum['getattachperm']);

修改为：

1. $allowgetattach = !$discuz_uid || !empty($forum['allowgetattach']) || ($allowgetattach && !$forum['getattachperm']) || forumperm($forum['getattachperm']);