This event was sent only when an ES was changed by libvlc. It was not sent when
an ES was changed by the input thread. To fix this issue, listen to the
INPUT_EVENT_ES input event (that is sent when an ES is added/deleted/selected)
to detect an ES selection change.

We don't want to trigger callbacks for "video-es"/"audio-es"/"spu-es" variables
from the input_thread since it's also listening to these callbacks and we want
to avoid a selecting busy loop.