vegetation_patch features from datapacks can cause a crash by IllegalStateException

I was messing around with the `vegetation_patch` feature tonight and encountered several crashes when generating chunks containing this feature.

To reproduce:

(1) Install the attached datapack Archive-1.zip

(2) Run /locatebiome terralith:cave/frozen_crystal_caves

(3) Teleport to the biome

(4) Observe crash