Add a bounds check on AVProbeData input.

patch by Ronald S. Bultje, rbultje ronald.bitfreak net
thread:
Date: Sat, 09 Jun 2007 19:22:17 -0400
Subject: [FFmpeg-devel] lavf probing

Originally committed as revision 9275 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/utils.c

@@ -1936,7 +1936,7 @@ int av_find_stream_info(AVFormatContext *ic)
                 }
             }
         }else if(st->codec->codec_type == CODEC_TYPE_AUDIO) {
-            if (st->codec->codec_id == CODEC_ID_NONE) {
+            if (st->codec->codec_id == CODEC_ID_NONE && probe_data[st->index].buf_size > 0) {
                 codec_identified[st->index] = set_codec_from_probe_data(st, &(probe_data[st->index]), 0);
                 if (codec_identified[st->index]) {
                     st->need_parsing = AVSTREAM_PARSE_FULL;