write_centerlines should work when centerlines are missing (#968)
write_centerlines should work when centerlines are missing (#968)


juliaeis/oggm,juliaeis/oggm,bearecinos/oggm,OGGM/oggm,bearecinos/oggm,TimoRoth/oggm,anoukvlug/oggm,anoukvlug/oggm,OGGM/oggm,TimoRoth/oggm