`EmptyWorld.INSTANCE` has a `null` `currentDimension()` because its static initializer has a cyclic dependency with `EmptyDimension`

[NotStirred]

This bug is currently not that bad, but if a chunky or a plugin were to ever classload EmptyDimension before EmptyWorld, currentDimension could be null which crashes everything.

Not really sure how to fix this, I guess we could give EmptyDimension a null world, but that means possible NPEs if its world is ever accessed