for a reason i can just assume some key events can vanish from the
event chain and mpv seems unresponsive.
after quite some testing i could confirm that the events are present at
the first entry point of the event chain, the sendEvent method of the
Application, and that they vanish at a point afterwards. now we use
that entry point to grab keyDown and keyUp events. we also stop
propagating those key events to prevent the no key input' error sound.
if we ever need the key events somewhere down the event chain we need
to start propagating them again. though this is not necessary currently.
