It is very annoying that atlas requires special handling with the map settings and we don't have a good way to test this.
This patch doesn't fix the atlas problem, but maybe streamlines the js side a bit more?
Changes: automatically test if the fallback is valid when loading the biome in the regular game (shouldn't impact performance in any significant way) and also simplify the if (g_MapSettings.Biome) ...
Now we can just run a script to generate each map once and see if any errors pop up.