moreFortressSpawningBlocks stops fortress mob spawning in bigger bounding box

[RubixDev]

When the moreFortressSpawningBlocks rule is set to off, which is the default, it should behave like vanilla: fortress mobs spawn on any block in the smaller bounding box and only on nether bricks in the bigger one. It does however stop fortress mob spawning outside the smaller box entirely. This happened while updating the code to 1.17.

Reported by JezaGaia: https://www.curseforge.com/minecraft/mc-mods/Rug?comment=12