Merge commit '05a4bacb'

* commit '05a4bacb':
  avpacket: Error out when creating 0-sized side data

This commit is a noop, see 5a633ec2

AV_PKT_DATA_METADATA_UPDATE can be zero sized in order to clear old
meta.

Note: maybe we could add a start or end marker.
Merged-by: Clément Bœsch <u@pkh.me>