Cron fails if comment module not installed

Solution looks like this (check with module_exists):

/**
 * Handle backlog of comments.
 */
function ip_backlog_comments() {
  if (module_exists('comment')) {
    $result = db_query_range(
      "SELECT c.cid AS cid, c.hostname AS hostname" .
      " FROM {comment} c" .
      " LEFT JOIN {ip_posts} i" .
      " ON i.type = 'comment'" .
      " AND (c.cid = i.id OR i.id IS NULL)" .
      " WHERE i.id IS NULL" .
      " ORDER BY c.cid DESC",
      0,
      50
    );
    foreach ($result as $row) {
      ip_posts_insert('comment', $row->cid, $row->hostname);
    }
  }
}