idcinvideo: correctly set AVFrame defaults
idcin: validate header parameters

Avoids using unsupported parameters and signed integer overflows.
idcin: fix check for presence of an audio stream
idcin: set channel_layout
idcin: set start_time and packet duration instead of manually tracking pts.

Also, use 1 / sample_rate for audio stream time_base.
idcin: set AV_PKT_FLAG_KEY for video packets with a palette
idcin: allow seeking back to the first packet

Also, do not allow seek-by-byte, as there is no way to find the next packet
boundary.
idcin: check for integer overflow when calling av_get_packet()

chunk_size is unsigned 32-bit, but av_get_packet() takes a signed int as the
packet size.
idcin: better error handling

Add some additional checks for EOF and print error messages on an incomplete
header or packet.

FATE reference updated for id-cin-video due to the demuxer no longer
returning a partial video packet at EOF.
idcin: return 0 from idcin_read_packet() on success.

This matches the AVInputFormat.read_packet() API.