Don't export null depth to PLY
Don't export null depth to PLY

mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM,oscarlorentzon/OpenSfM,oscarlorentzon/OpenSfM,oscarlorentzon/OpenSfM,oscarlorentzon/OpenSfM,mapillary/OpenSfM