Dimension-specific world spawn point causes mob spawning in other dimensions to fail

Reproduction:

1. In a default world, tp to nether or end and observe no mobs spawning (except ones that come with the terrain like striders in the nether)

2. Set the world spawn point to the nether or end to see mobs spawning in that dimension, tp back to the other dimensions or back to the overworld to see mobs no longer spawning there unless we set the world spawn back to those dimensions again.