Most variables not working on forumdisplay_thread

[XP Mai]

This is custom, nation's link.
(I'm doing this for a game.)

OK, we are going to name it $thread['fid5'] (so that is the name to be used in the template).
In script forumdisplay.php gp to line 1315 which reads:

$plugins->run_hooks("forumdisplay_thread_end");

Directly before that add the following 2 lines:

$query = $db->simple_select("userfields", "fid5", "ufid = {$thread['uid']}");
$thread['fid5'] = $db->fetch_array($query)['fid5']; 

Try this out together with $thread['username']. When these work fine we can go to the avatar.

The forum becomes white until I remove the code.