Special Character in Username

[veemon]

Hey there!
I implented a new site with a login script I found in this forum and everything worked nicely, until someone with a special character (♥) tried to login.
I absolutely can't seem to find the error here.
The $username shows it correctly if I echo it and it's correctly displayed in the database as well.
The problem seems to be when getting the $data.
When dumping it I noticed that it would just return a false boolean when I tried logging in with the ♥ character.
Thanks in advance for any help!

Here is the script:

        $startTime = microtime(true);
       
        require('../library/XenForo/Autoloader.php');
        XenForo_Autoloader::getInstance()->setupAutoloader('../library');
       
        XenForo_Application::initialize('../library');
        XenForo_Application::set('page_start_time', $startTime);
       
        $username = $_POST['username'];
        $password = $_POST['password'];
       
        $db = XenForo_Application::getDb();
       
        $data = $db->fetchOne('
            SELECT
                auth.data
            FROM xf_user_authenticate AS auth
            INNER JOIN xf_user AS user ON
                (user.user_id = auth.user_id)
            WHERE user.username = ?
        ', $username);
       
        $id = $db->fetchOne('SELECT user_id FROM xf_user WHERE username = ?', $username);
       
        $auth = XenForo_Authentication_Abstract::createDefault();
       
        $auth->setData($data);
       
        $check = $auth->authenticate($username, $password);
       
        var_dump($data);
        if($check) {
            session_start();
           
            /*redirect('gamesite/protected/')*/;
        } else {
            /*redirect('gamesit/index.php?message=2')*/; 
        }