If you REDIT a room with autogenerated elevator exits, they are overwritten

[luciensadi]

Current behavior:

• If exit existed previously and was overwritten by elevator: Restore that prior exit.
• If exit did not exist: Exit to 0.

Expected behavior: Leave the elevator exits alone-- we may need to have the elevator overwrite the world data if this is an issue instead of just plopping in ad-hoc non-saving exits.