lavfi/buffersink: check av_frame_ref() failure.
lavf/concatdec: fix possible leak in case of malloc failure.

Fix CID 747737.
lavf: avformat_seek_file(): validate stream_index.
lavu/frame: use channels rather than channel_layout.
Merge remote-tracking branch 'cigaes/master'

* cigaes/master:
  lavu/frame: use channels rather than channel_layout.
  lavf: avformat_seek_file(): validate stream_index.
  lavf/concatdec: fix possible leak in case of malloc failure.
  lavfi/buffersink: check av_frame_ref() failure.

Merged-by: Michael Niedermayer <michaelni@gmx.at>