dashdemux: Consistently skip audio stream depending on TRICKMODE_NO_AUDIO
Submitted by Seungha Yang
If TRICKMODE_NO_AUDIO flag was set, audio stream can never ever be exposed.
Meanwhile, per live mpd update, internal seeking is performed to sync
last stream entry with new one. At that time, mismatch among them can be possible
because audio streams in last stream entry were ignored by TRICKMODE_NO_AUDIO.