core: Only notify for GDataService::authenticated if it's actually changed
core: Only notify for GDataService::authenticated if it's actually changed

Pecisk/libgdata,pwithnall/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata-gtasks,Distrotech/libgdata,GNOME/libgdata,Pecisk/libgdata,pwithnall/libgdata,Distrotech/libgdata,Distrotech/libgdata,Pecisk/libgdata-gtasks