fix: generate support roof for models lower than support roof thickness (CURA-3821, CURA-3744)
fix: generate support roof for models lower than support roof thickness (CURA-3821, CURA-3744)

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