evdev: Ignore key/button release events if key was never pressed

evdev: Ignore key/button release events if key was never pressed

The kernel may send a 'release' event without ever having sent a key
'pressed' event in case the key was pressed before libinput was
initiated. Ignore these events so that we always guarantee a release
event always comes after a pressed event for any given key or button.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>