wayland: Don't try to create a subsurface again
wayland: Don't try to create a subsurface again

We already did that inside gdk_wayland_window_create_surface() that's
called 2 lines above.

https://bugzilla.gnome.org/show_bug.cgi?id=738912

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