Guard against invalid memory read

Originally committed as revision 22207 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/bink.c

@@ -210,7 +210,7 @@ static int read_packet(AVFormatContext *s, AVPacket *pkt)
         }
         bink->remain_packet_size -= 4 + audio_size;
         bink->current_track++;
-        if (audio_size > 0) {
+        if (audio_size >= 4) {
             /* get one audio packet per track */
             if ((ret = av_get_packet(pb, pkt, audio_size))
                                            != audio_size)
@@ -223,6 +223,8 @@ static int read_packet(AVFormatContext *s, AVPacket *pkt)
             bink->audio_pts[bink->current_track -1] +=
                 AV_RL32(pkt->data) / (2 * s->streams[bink->current_track]->codec->channels);
             return 0;
+        } else {
+            url_fseek(pb, audio_size, SEEK_CUR);
         }
     }