Fix cascade worldgen from Thaumcraft

[Pilzinsel64]

Relevant snippet from stack trace:

at Launch//thaumcraft.common.lib.world.ThaumcraftWorldGenerator.createRandomNodeAt(ThaumcraftWorldGenerator.java:304) ~[ThaumcraftWorldGenerator.class:?]
at Launch//thaumcraft.common.lib.world.ThaumcraftWorldGenerator.generateSurface(ThaumcraftWorldGenerator.java:376) ~[ThaumcraftWorldGenerator.class:?]
at Launch//thaumcraft.common.lib.world.ThaumcraftWorldGenerator.worldGeneration(ThaumcraftWorldGenerator.java:109) ~[ThaumcraftWorldGenerator.class:?]
at Launch//thaumcraft.common.lib.world.ThaumcraftWorldGenerator.generate(ThaumcraftWorldGenerator.java:95) ~[ThaumcraftWorldGenerator.class:?]