Disable parsing for ogg streams where no ogg header was found,

if no header was found the parser was not initialized and thus will
crash when trying to use it.

Originally committed as revision 20093 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/oggdec.c

@@ -477,12 +477,17 @@ static int
 ogg_read_header (AVFormatContext * s, AVFormatParameters * ap)
 {
     struct ogg *ogg = s->priv_data;
+    int i;
     ogg->curidx = -1;
     //linear headers seek from start
     if (ogg_get_headers (s) < 0){
         return -1;
     }
 
+    for (i = 0; i < ogg->nstreams; i++)
+        if (ogg->streams[i].header < 0)
+            ogg->streams[i].codec = NULL;
+
     //linear granulepos seek from end
     ogg_get_length (s);