[youtube] Add missing precondition
[youtube] Add missing precondition

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