BUG: Ensure that window length value is sanity checked.
BUG: Ensure that window length value is sanity checked.

When moving BatchTransform off of EventWindow as a base object,
the checking of window length was lost, restore that check using
the same function as EventWindow.

MonoCloud/zipline,magne-max/zipline-ja,erikness/AlephOne,CarterBain/AlephNull,joequant/zipline,chrjxj/zipline,ronalcc/zipline,enigmampc/catalyst,magne-max/zipline-ja,bartosh/zipline,dmitriz/zipline,mattcaldwell/zipline,joequant/zipline,ChinaQuants/zipline,chrjxj/zipline,dhruvparamhans/zipline,humdings/zipline,wubr2000/zipline,YuepengGuo/zipline,DVegaCapital/zipline,dmitriz/zipline,davidastephens/zipline,nborggren/zipline,michaeljohnbennett/zipline,kmather73/zipline,mattcaldwell/zipline,stkubr/zipline,CDSFinance/zipline,Scapogo/zipline,nborggren/zipline,morrisonwudi/zipline,ChinaQuants/zipline,iamkingmaker/zipline,stkubr/zipline,grundgruen/zipline,keir-rex/zipline,YuepengGuo/zipline,florentchandelier/zipline,quantopian/zipline,AlirezaShahabi/zipline,enigmampc/catalyst,CarterBain/AlephNull,cmorgan/zipline,sketchytechky/zipline,aajtodd/zipline,alphaBenj/zipline,otmaneJai/Zipline,kmather73/zipline,aajtodd/zipline,dkushner/zipline,zhoulingjun/zipline,umuzungu/zipline,semio/zipline,otmaneJai/Zipline,quantopian/zipline,gwulfs/zipline,AlirezaShahabi/zipline,jordancheah/zipline,keir-rex/zipline,jimgoo/zipline-fork,ronalcc/zipline,StratsOn/zipline,humdings/zipline,DVegaCapital/zipline,michaeljohnbennett/zipline,erikness/AlephOne,wilsonkichoi/zipline,jordancheah/zipline,dkushner/zipline,dhruvparamhans/zipline,bartosh/zipline,StratsOn/zipline,euri10/zipline,grundgruen/zipline,Scapogo/zipline,MonoCloud/zipline,CDSFinance/zipline,wilsonkichoi/zipline,cmorgan/zipline,alphaBenj/zipline,semio/zipline,sketchytechky/zipline,zhoulingjun/zipline,euri10/zipline,gwulfs/zipline,iamkingmaker/zipline,umuzungu/zipline,jimgoo/zipline-fork,morrisonwudi/zipline,florentchandelier/zipline,davidastephens/zipline,wubr2000/zipline