Fix: Desert/rainforest data coordinate 'y' is off by 1 when their 'x' coordinate is negative #8588
Motivation / Problem
The data that is used for generating desert or rainforest in sub-tropical is a list of TileIndexDiffC offsets, and visually look like a circumference.
This PR fixes the offset layout in the same manner as the oil rig layout.
Checklist for review
Some things are not automated, and forgotten often. This list is a reminder for the reviewers.