skip packet if no stream index is found, fix proxy_pal030926.mxf

Originally committed as revision 6721 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mxf.c

@@ -265,6 +265,7 @@ static int mxf_read_packet(AVFormatContext *s, AVPacket *pkt)
             int index = mxf_get_stream_index(s, &klv);
             if (index < 0) {
                 av_log(s, AV_LOG_ERROR, "error getting stream index\n");
+                url_fskip(&s->pb, klv.length);
                 return -1;
             }
             /* check for 8 channels AES3 element */