[Experimental] Amethyst Geode doesn't generate on negative Y levels / below Y=0

Amethyst Geode on Java Edition can be found on negative Y levels or below Y=0. However, on Bedrock Edition, you cannot find that below Y=0, which breaks parity and consistency with other structures that generate below Y=0.

Step to Reproduce
1. Find any geodes below Y=0 if possible.
2. Compare it with Java Edition, see if you can find it.

Expected Result
Amethyst geodes can generate below Y=0 / on negative Y.

Observed Result
Amethyst geodes don't generate below Y=0 / on negative Y.