Re-do minimum combine_infill_layers check
Re-do minimum combine_infill_layers check

This was accidentally removed in the merge...
markwal/CuraEngine,pratikshashroff/pcura,alephobjects/CuraEngine,totalretribution/CuraEngine,ROBO3D/CuraEngine,markwal/CuraEngine,totalretribution/CuraEngine,Ultimaker/CuraEngine,pratikshashroff/pcura,ROBO3D/CuraEngine,alephobjects/CuraEngine,pratikshashroff/pcura,Ultimaker/CuraEngine,alephobjects/CuraEngine,ROBO3D/CuraEngine,markwal/CuraEngine,totalretribution/CuraEngine