Notice: Undefined offset: 0 in advanced_forum_get_reply_link() line 815 of advanced_forum/advanced_forum.module

When I preview a comment then clear all caches this error is shown when I refresh the preview comment page.

If I then backtrack to the forum then click the topic then add a comment and preview the error disappears.

The reply to button is not shown on the preview so maybe that has something to do with it when re-establishing the cached version of the forum.

the following is the code from the module

 800 function advanced_forum_get_reply_link($node) {
 801   $reply_link = array();
 802
 803   $comment_setting = $node->comment;
 804   $fragment = 'comment-form';
 805
 806   if ($comment_setting == COMMENT_NODE_OPEN) {
 807
 808     $allowed = false;
 809     if (module_exists('forum_access')) {
 810       // get tid
 811       if (!empty($node->taxonomy_forums)) {
 812         reset($node->taxonomy_forums);
 813         $langcode = key($node->taxonomy_forums);
 814         if (!empty($node->taxonomy_forums[$langcode])) {
 815           $tid =  $node->taxonomy_forums[$langcode][0]['tid'];
 816           if (forum_access_access('create', $tid)) {
 817             $allowed = true;
 818           }
 819         }
 820       }
 821     }
 822     else {
 823       $allowed = user_access('post comments');
 824     }