If the game steps forward, entities could be moving around, so we need
to wipe the memoized character vision.
Change-Id: If6ea6a8c4bed7aefef90a0a2ab17eff0af9b9bbe
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3215
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI