gdkseatdefault: Don't hide GdkWindow on grab failure
Application is not expecting that.
Bug found due gdk_seat_grab() failure on Lock Screen. When user Unlock the screen, the application is visible but does not receive enter-event any more on X11/GNOME.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1485968 Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1571422
Signed-off-by: Victor Toso victortoso@redhat.com