Reworked the hacks required to avoid assertion when travel moves are added before insets.
Reworked the hacks required to avoid assertion when travel moves are added before insets.

So now it adds a bogus zero length extrude immediately after the move to the z seam location
and this stops the assertion occurring. Still don't understand the root cause of this.

Anyway, the good news is that it means that the z seam of the inner insets will be located
very close to the z seam of the outer inset and this should cut out a lot of travel moves.

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