Only set support extruders to be used if support is enabled
Only set support extruders to be used if support is enabled

We know this beforehand too.

Contributes to issue CURA-3443.

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