Fixing issue #77
Fixing issue #77

container.offset() can be undefined. Calling top over that was generating an error.
sroze/ngInfiniteScroll,xuwupeng2000/ngInfiniteScroll,tianyawy/ngInfiniteScroll,sroze/ngInfiniteScroll,itkin/ngInfiniteScroll,just-boris/ngInfiniteScroll,solomon87/ngInfiniteScroll,seawenzhu/ngInfiniteScroll,uzen/angular-infinitescroll,cloudnode-app/ngInfiniteScroll,maxamillion32/ngInfiniteScroll,uzen/angular-infinitescroll,msbit/ngInfiniteScroll,Tradiio/ngInfiniteScroll,Masadow/ngInfiniteScroll,AmitThakkar/ngInfiniteScroll,timesqueezer/ngInfiniteScroll,suryasingh/ngInfiniteScroll,aisharagheb/ngInfiniteScroll,yesmeck/ngInfiniteScroll,maksimr/ngInfiniteScroll,Manumental32/ngInfiniteScroll