setupTerrain will loop until (among other conditions) the chunksToUpdate set is
empty. However its size is never decreased during setupTerrain.
Having a (backwards) jump in time right before rendering the first frame would
reset the RenderGlobal due to the world change, leaving the chunksToUpdate set
empty to begin with and due to other changes, chunks are never inserted into it
during rendering (because they're always updated immediately).
The new screenshot feature and rendering a path that's in the future will not
trigger any world change, leaving the render process stuck in a life lock.
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