vB4 to vB3 plugin syntax help?

[kpmedia]

I found a simple vB4 plugin that does what I need ... but I'm on vB3.8.x

PHP Code:

$current_thread = $thread['threadid'];
$query = $vbulletin->db->query_first_slave("
    SELECT user.usergroupid, user.membergroupids
    FROM " . TABLE_PREFIX . "thread AS thread
    LEFT JOIN " . TABLE_PREFIX . "user AS user ON (user.userid = thread.firstpostid)
    WHERE thread.threadid = " . $current_thread . "
    ");
$primary_group = $query['usergroupid'];
$secondary_groups = $query['membergroupids'];
if(!empty($secondary_groups)) {
    $groups = $primary_group . "," . $secondary_groups;
} else {
    $groups = $primary_group;
}    
$groups_all = explode(",", $groups);
vB_Template::preRegister('threadbit',array('group' => $groups_all)); 


It's from this thread: https://vborg.vbsupport.ru/showthread.php?t=295306 (post#11 and down)

This plugin causes vB3.8.9 to load a blank screen for the threadbit display page.

I think the problem is the last time, when it registers the variable.

Help?