Superflat worlds start generating at negative coordinates, causing a dark horizon

Flat worlds start to generate in negative coordinates, making a unpleasant view to the world

To reproduce

1. Create a flat world in 21w06a
2. Enter to the world
3. Press f3 and you spawn in negative coordinates

Observed Results:
You spawn in negative coordinates giving an unpleasant void view

Expected Results:
Generates at coordinate 4, or that the black edge of the void is not visible