Fix bug in GCodeExport::writeExtrusion() - it no longer includes z hop height in extrusion length.
Fix bug in GCodeExport::writeExtrusion() - it no longer includes z hop height in extrusion length.

It was using a 3d vector length that included the z hop height when it only should have
been just 2d.

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