oggdec: Leave treatment of serial changes to the decoder.

Attempting to re-parse the headers at demuxer level is a
pandora box the way its done currently.

This allows full reconfiguration of vorbis streams

Fixes Ticket2117
Fixes Ticket2121
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggdec.c

@@ -184,6 +184,9 @@ static int ogg_replace_stream(AVFormatContext *s, uint32_t serial)
 
     os = &ogg->streams[0];
 
+    os->serial  = serial;
+    return 0;
+
     buf     = os->buf;
     bufsize = os->bufsize;
     codec   = os->codec;