dashdemux2: fix mpeg-ts issue with no audio output
requested to merge elliot_chen/gstreamer:dashdemux2-support-mpeg-ts-audio-playback-function into main
- For dashdemux2, one stream will create one track. Only video track can be created for mpeg-ts stream.
- Add the function to check and create the other track if needed.
Fixes #2593 (closed)
Edited by Edward Hervey