Clean-up idle handler when leaving the open_host_idle()
Clean-up idle handler when leaving the open_host_idle()

An explicit yield back to the channel coroutine when the idle function
is still pending will leave it in the background, referencing objects
that may no longer exist. Make sure we remove it when
channel_open_host() is resumed.

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