Forge version: 14.23.52815
Twilight Forest version: 3.8.689
Link to stall report: here

Steps to reproduce:

1. Generate a Twilightforest Fireswamp biome in a void world.

What I expected to happen:
It not stalling

What happened instead:
When generating a Twilightforest Biome in a void world, it generates vines, but this loop never ends because in a void world, there is no block, that would stop the loop.

I suggest adding another check to the loop adding && down.getY() >= 0