Masonry, isotope, packery images overlapping in Safari

There seems to be an issue with images loading and infinite scroll in Safari. On first load of your [infinitescroll masonry demo](https://codepen.io/desandro/pen/eRRQVo), images are "behind" the colored blocks. On subsequent loads, the layout is as expected (After images are cached, it does not occur).
I can reproduce it using a new tab in Safari's "private window" setting consistently. Does not seem to occur in Firefox or Chrome.

Mike

Start by reproducing the linked infinite-scroll Masonry demo in Safari private browsing with uncached images, comparing the first load with subsequent loads and other browsers. Investigate the image-loading and infinite-scroll interaction; done means images no longer appear behind the colored blocks on the initial load.

Written by the indexing model from the issue text.