Properly checking if timezone is set
Properly checking if timezone is set

Current code will "change" properly set timezone using `date_default_timezone_set('Europe/Warsaw');` which is date.timezone equivalent in code (you can either set timezone in code or php.ini).

date.timezone is a fallback while using: `date_default_timezone_get()`:http://php.net/manual/pl/function.date-default-timezone-get.php
mk-j/PHP_XLSXWriter,mk-j/PHP_XLSXWriter