Void effects incorrectly given under bedrock if min_y isn't 0

The bug

The visual effects (darkening of the skybox) of the void are fixed to happen at and below y=0. With custom worlds you can change the min_y of worlds.

To reproduce

1. Load min_y0 in the attachments
2. Go below bedrock
3. →  Everything below bedrock, the moon and stars are darkened out by the void effects.
   
4. Load min_y16
5. /time set night
6. Go below bedrock
   →  The sky isn't darkened out by the void effects directly below bedrock
   
7. It is darkened out if you go below y=0 again.