ext/ffmpeg/gstffmpegdec.c: When H264 is presented without codec_data, use a parser to frame it by assuming that no co...

Original commit message from CVS:
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_open),
(gst_ffmpegdec_chain):
When H264 is presented without codec_data, use a parser to frame it
by assuming that no codec_data implies it is unpacketised.
Always use the return value from the parser to advance the input
buffer position.