gtk: calling connect() on a connecting channel is fine
gtk: calling connect() on a connecting channel is fine

This avoid problems where different display shares the same input
channel and try to connect two times.

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