bugfix naive time estimate (CURA-415)
bugfix naive time estimate (CURA-415)

ROBO3D/CuraEngine,totalretribution/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,pratikshashroff/pcura,pratikshashroff/pcura,alephobjects/CuraEngine,totalretribution/CuraEngine,alephobjects/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,totalretribution/CuraEngine,pratikshashroff/pcura,Ultimaker/CuraEngine