Merge commit '09ae7b81ea2051eec2be9964296bd6ef492c6622'

* commit '09ae7b81ea2051eec2be9964296bd6ef492c6622':
  flvdec: do not create any streams in read_header()

Not merged. The demuxer issues warnings when a new stream is encountered
and reading the metadata requires that streams already exist.

Merged-by: Hendrik Leppkes <h.leppkes@gmail.com>