Mapbox layer doesn't allow much zoom in

[rsargent]

Max zoom computation seems broken for mapbox layers

Example: https://staging.earthtime.org/explore#v=-1.78111,-15.61643,-0.058,latLng&t=1.7&ps=50&l=blsat,bdrkmb,mb_cities&bt=19840101&et=20191231&startDwell=0&endDwell=0

Max zoom in is limited to:

[rsargent]

Resolved with 3aebf21805a3ef7e4ca1543d9ad4c4e976b58e0d