fix: only handle support mesh if present (CURA-3416)
fix: only handle support mesh if present (CURA-3416)

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