Update oxsession.php and loads oxBasket through oxNew()

The moved line "$oEmptyBasket = oxNew('oxbasket');" was an old design flaw. The old line leads to an intialization through oxAutoload because the unserialize() is called first, but normally, every class is initialized through oxNew(). This can break modules. (Broke mine many times!)
(cherry picked from commit 0a6f2ac)