Amethyst geodes are cut off on Y=0 when loading a 1.17.1 world in 1.18

When converting a 1.17.1 world to the new version, an amethyst geode can generate at Y=-3. In this case, it is only generated below the original world and Y>0 is not affected.

I suggest generating amethyst geodes only at heights Y<-10 when converting from an older world.