@Arianguy
You can change these lines to the following:
elseif ($tz !== 'UTC' && strpos($tz, '/') === false) {
return 'Asia/Dubai';
// Attempt to lookup based on the abbreviation
//if (!($tz = timezone_name_from_abbr($tz)))
// Abbreviation doesn't point to anything valid
//return $default;
}
Keep in mind though that you'll have to re-apply these changes every time you upgrade osTicket.
Cheers.