gtk3x: Get rid of gdk_device_get_state() call
gtk-3.99.0 (or already gtk-3.98.5, which I failed to build) drops gdk_device_get_state(). Replace a call in gtk3x-client.
gtk-3.99.0 (or already gtk-3.98.5, which I failed to build) drops gdk_device_get_state(). Replace a call in gtk3x-client.