100l, av_read_packet must check for read_packet error, in case of

error pkt->stream_index could be invalid and must not be used.
Fixes a crash with http://www.cs.berkeley.edu/~dmolnar/2-snippet3.wav


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@11307 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/utils.c

@@ -497,6 +497,8 @@ int av_read_packet(AVFormatContext *s, AVPacket *pkt)
     AVStream *st;
     av_init_packet(pkt);
     ret= s->iformat->read_packet(s, pkt);
+    if (ret < 0)
+        return ret;
     st= s->streams[pkt->stream_index];
 
     switch(st->codec->codec_type){