Fix not slicing refreshing after deleting last object from loaded project file. CURA-3559
Fix not slicing refreshing after deleting last object from loaded project file. CURA-3559

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