updated write to check scenario exists before adding varients
updated write to check scenario exists before adding varients

tomalrussell/smif,willu47/smif,tomalrussell/smif,willu47/smif,nismod/smif,nismod/smif,willu47/smif,nismod/smif,tomalrussell/smif,willu47/smif,nismod/smif,tomalrussell/smif