avcodec: video: fallback in case of hw error

This is only used for the AV1 HW module. A va error is possible and need to be handled (even if unlikely).

In case of error, it will fall back to the next decoder module (dav1d or avcodec sw), but the first blocks are already consumed by the hw module, therefore there will be a 1 to 10sec lag before displaying the first picture.

One other solution would be to switch to single threaded avcodec sw directly.