corrected wrong initialization in polygon.cpp
corrected wrong initialization in polygon.cpp

alex1818/CuraEngine,uus169/CuraEngine,alephobjects/CuraEngine,jacobdai/CuraEngine-1,markwal/CuraEngine,uus169/CuraEngine,electrocbd/CuraEngine,derekhe/CuraEngine,alex1818/CuraEngine,totalretribution/CuraEngine,electrocbd/CuraEngine,markwal/CuraEngine,pratikshashroff/pcura,mspark93/CuraEngine,ROBO3D/CuraEngine,patrick3coffee/CuraTinyG,alephobjects/CuraEngine,uus169/CuraEngine,alex1818/CuraEngine,pratikshashroff/pcura,totalretribution/CuraEngine,alephobjects/CuraEngine,electrocbd/CuraEngine,patrick3coffee/CuraTinyG,ROBO3D/CuraEngine,fxtentacle/CuraEngine,totalretribution/CuraEngine,mspark93/CuraEngine,jacobdai/CuraEngine-1,fxtentacle/CuraEngine,derekhe/CuraEngine,jacobdai/CuraEngine-1,pratikshashroff/pcura,Ultimaker/CuraEngine,mspark93/CuraEngine,patrick3coffee/CuraTinyG,fxtentacle/CuraEngine,markwal/CuraEngine,Ultimaker/CuraEngine,ROBO3D/CuraEngine,derekhe/CuraEngine