quartz-dnd: make sure to set source window
quartz-dnd: make sure to set source window

https://bugzilla.gnome.org/show_bug.cgi?id=658722

ahodesuka/gtk,alexlarsson/gtk,jigpu/gtk,Lyude/gtk-,Adamovskiy/gtk,Lyude/gtk-,chergert/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,Adamovskiy/gtk,grubersjoe/adwaita,grubersjoe/adwaita,davidgumberg/gtk,jessevdk/gtk,chergert/gtk,ahodesuka/gtk,davidgumberg/gtk,chergert/gtk,ahodesuka/gtk,alexlarsson/gtk,davidgumberg/gtk,jigpu/gtk,ahodesuka/gtk,Adamovskiy/gtk,jigpu/gtk,chergert/gtk,chergert/gtk,jigpu/gtk,Adamovskiy/gtk,jessevdk/gtk,jadahl/gtk,jessevdk/gtk,davidgumberg/gtk,ahodesuka/gtk,jadahl/gtk,Lyude/gtk-,alexlarsson/gtk,grubersjoe/adwaita,jessevdk/gtk,ahodesuka/gtk,jadahl/gtk,jessevdk/gtk,davidgumberg/gtk,Lyude/gtk-,ahodesuka/gtk,grubersjoe/adwaita,grubersjoe/adwaita,Lyude/gtk-,chergert/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,jigpu/gtk,grubersjoe/adwaita,ahodesuka/gtk,jigpu/gtk,Adamovskiy/gtk,Adamovskiy/gtk,davidgumberg/gtk,Adamovskiy/gtk,alexlarsson/gtk,alexlarsson/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,jessevdk/gtk,jadahl/gtk,chergert/gtk,Lyude/gtk-,davidgumberg/gtk,jadahl/gtk,chergert/gtk,alexlarsson/gtk,jessevdk/gtk,Lyude/gtk-,Lyude/gtk-,grubersjoe/adwaita,jigpu/gtk