Do not crash if we try to send polygons after we've already sent them
Do not crash if we try to send polygons after we've already sent them

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