fix: erase with impossible iterator when trying to simplify an empty polygon (CURA-1430)
fix: erase with impossible iterator when trying to simplify an empty polygon (CURA-1430)

ROBO3D/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,Ultimaker/CuraEngine,totalretribution/CuraEngine,ROBO3D/CuraEngine,totalretribution/CuraEngine