fix: initialize slicer members to invalid values
fix: initialize slicer members to invalid values

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