coroutine: reference object when signaling
coroutine: reference object when signaling

Before the signal is actually emitted, the channel may be
released. Let's keep a reference to the object during
the function time, to prevent the object from being destroyed before
calling g_signal_emit() or g_object_notify() in main context.

freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,guodong/spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,elmarco/spice-gtk,fgouget/spice-gtk,SPICE/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,flexVDI/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk