$query = $pawn->get("SELECT senduid, recuid FROM chat WHERE senduid='{$userData['u_id']}' OR recuid = '{$userData['u_id']}'");

$displayedUids = array();

foreach($query as $data) {
    if ($data['senduid'] == $userData['u_id'] && !in_array($data['recuid'], $displayedUids)) {
        echo $data['recuid']."<br>";
        $displayedUids[] = $data['recuid'];
    } elseif ($data['recuid'] == $userData['u_id'] && !in_array($data['senduid'], $displayedUids)) {
        echo $data['senduid']."<br>";
        $displayedUids[] = $data['senduid'];
    }
}