Validate / sanitize $sort parameter

[tmuras]

\mod_oublog_external::get_blog_allposts_parameters accepts $sort parameter of type PARAM_TEXT.

This is then passed to: oublog_import_getallposts($params['blogid'], $params['sort'],

Where it's used as:

    $sql = "SELECT p.id, p.timeposted, p.title
        FROM {oublog_posts} p
        INNER JOIN {oublog_instances} bi on bi.id = p.oubloginstancesid
        $tagjoin
        WHERE bi.userid = ?
        AND bi.oublogid = ?
        AND p.deletedby IS NULL
        $tagwhere
        ORDER BY p." . $sort;

It would be a good idea to sanitize / validate the value of $sort before concatenation.