fix auto-scroll calculation
fix auto-scroll calculation

grandmanitou/fancytree,Koloto/fancytree,hglty07/fancytree,Aliccer/fancytree,jiangjunt/fancytree,spilmert/fancytree,dewhisna/fancytree,HobieCat/fancytree,grandmanitou/fancytree,jiangjunt/fancytree,spilmert/fancytree,Mats0/fancytree,Aliccer/fancytree,dewhisna/fancytree,Koloto/fancytree,jiangjunt/fancytree,HobieCat/fancytree,HobieCat/fancytree,Koloto/fancytree,instein2014/JQuery,dewhisna/fancytree,Aliccer/fancytree,grandmanitou/fancytree,instein2014/JQuery,spilmert/fancytree,Mats0/fancytree,hglty07/fancytree,hglty07/fancytree