Also retract if outer wall is the only wall
Also retract if outer wall is the only wall

Because we need to retract if we're moving towards an outer wall. If there is only one wall, that is always the outer wall.

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