Do not add an extruder if it has no position set
Do not add an extruder if it has no position set

Otherwise we get very weird values in the extruders dict

Contributes to CURA-3738

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