Overlays do not load if zoomed beyond 20.42

[itspangler]

issue

this feels like a pretty niche problem, not an urgently needed fix, but i wanted to note it: layer loading isn't triggered on overlay layers that are zoomed in at a depth of 20.42 or greater at the time the layer is requested. once you hit 20.42, OL starts looking for zoom level 21, and it can't load an overlay. for instance:

• this loads
• this doesn't load

the layer loads if you zoom back out to a depth of 20.41 or lower, because OL starts looking for tiles at a depth of 20. this is reproducible anywhere in Atlascope by 1) zooming in deeply to somewhere on Atlascope and 2) switching the overlay to a new atlas layer

possible fix

i couldn't puzzle anything out, but there should be a way to force a layer to load at zoom level 20, no matter the zoom depth of the current view!