Slicer: Fixed usage of INVALID_TERMINUS value not going through constant.
Slicer: Fixed usage of INVALID_TERMINUS value not going through constant.

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