Lazy load for 1 item

If you need the lazy load feature, but you have only one picture, Slick do not try to load it because in this case

>  rangeStart = _.options.infinite ? _.options.slidesToShow + _.currentSlide : _.currentSlide;
> 1 + 0 = 1 

so the range is starting at 1, and your only picture will be ignored

Seems to create a big mess if you have more than 1 picture and infinite mode... working on it