Hide infill settings if infill density is 0
Hide infill settings if infill density is 0

Mostly to test, but this relation was missing anyway.

Contributes to issue CURA-2361.

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