Server crashes when setting the world spawn on a sublebel

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Description

Observed behavior

Using /setworldspawn to set the world spawn coordinates to a position within a sublevel causes the server to crash.

Expected behavior

New players should spawn on the sublevel when they join the server for the first time.

Game Log

https://mclo.gs/isLALN1

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This also bricks the world without NBT-editing the world spawn point to be outside the plotyard again.