gst-ffmpeg: fix CVE-2013-3674

gst-ffmpeg: fix CVE-2013-3674

The cdg_decode_frame function in cdgraphics.c in libavcodec in FFmpeg before
1.2.1 does not validate the presence of non-header data in a buffer, which
allows remote attackers to cause a denial of service (out-of-bounds array
access and application crash) via crafted CD Graphics Video data.

http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-3674

Signed-off-by: Ming Liu <ming.liu@windriver.com>
Signed-off-by: Jeff Polk <jeff.polk@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>