Handle pyramids with single `0` level

[katamartin]

When rendering a pyramid with only a single 0 level, it is not properly rescaled to render at when zoom >= 1 unlike the way the level 1 and higher tiles scale in pyramids with multiple levels. This might has to do with the way that offsets are calculated.

See the example behavior and source below:

https://carbonplan-data-viewer.s3.amazonaws.com/demo/leap-10-2023/web-mercator_pyramid_tasmax_day_ACCESS-CM2_historical_r1i1p1f1_gn.zarr