Update documentation for return of getExtruderValue
Update documentation for return of getExtruderValue

It now falls back to global instead of returning None.

Contributes to issue CURA-2024.

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