Use Z seam pos as starting point if Z seam is user-specified
Use Z seam pos as starting point if Z seam is user-specified

This should prevent a long travel move in some cases.

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