### A probe no longer panics on two adjacent start codes

- `wai.video.avs3` and `wai.audio.avs3`: a payload with a start code prefix directly after another (`00 00 01 00 00 01`)
  made the unit split slice backwards and panic, so a hostile payload could stop whatever probed it. It is now the empty
  unit format-probes §8.2 reads, and the payload is refused. A test now gives every probe 30,000 payloads of hostile bytes.

