BUG: fix `burn`/`post_burn` check
BUG: fix `burn`/`post_burn` check

guillochon/FriendlyFit,bmockler/MOSFiT,guillochon/MOSFiT,guillochon/MOSFiT,mnicholl/MOSFiT,mnicholl/MOSFiT,villrv/MOSFiT,bmockler/MOSFiT,guillochon/MOSFiT,mnicholl/MOSFiT,villrv/MOSFiT