fix: multVolumes: merge overlap better with model (CURA-2427)
fix: multVolumes: merge overlap better with model (CURA-2427)

when models where directly adjacent, the overlap area wouldn't be merged with the model at all places because of rounding errors

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