evdev: don't send frame events if we filtered the touch event

evdev: don't send frame events if we filtered the touch event

If the touch is inactive the seat_slot is -1 and we filter the event. The same
happens for devices that send may touch events but aren't touch devices like
any touch-capable mouse. In those cases we sent a bunch of 'empty' touch frame
events. Stop this by checking if we actually flushed the respective event.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>