Fix offsetting polygon in single extrusion
Fix offsetting polygon in single extrusion

In single extrusion, the machine_nozzle_offset_x and machine_nozzle_offset_y were not defined in the used extruder stacks, because the used extruder stack is the global stack.

Contributes to issue CURA-2625.

fieldOfView/Cura,hmflash/Cura,hmflash/Cura,ynotstartups/Wanhao,Curahelper/Cura,fieldOfView/Cura,Curahelper/Cura,ynotstartups/Wanhao