NullPointerException in ActiveSableCompanion.getTrackingSubLevel when opening a world with a Sable entity (sable 2.0.5)

### Context

When attempting to load an existing singleplayer world that contains an active Sable entity/sub-level, the game immediately crashes with a NullPointerException during the render tick.

### Crash Report

https://mclo.gs/IsBVoAC