Port r19426 from libvorbis.

Reject multiple headers of the same type.

info.c

@@ -227,7 +227,6 @@ static int _vorbis_unpack_comment(vorbis_comment *vc,oggpack_buffer *opb){
 static int _vorbis_unpack_books(vorbis_info *vi,oggpack_buffer *opb){
   codec_setup_info     *ci=(codec_setup_info *)vi->codec_setup;
   int i;
-  if(!ci)return(OV_EFAULT);
 
   /* codebooks */
   ci->books=oggpack_read(opb,8)+1;
@@ -367,6 +366,10 @@ int vorbis_synthesis_headerin(vorbis_info *vi,vorbis_comment *vc,ogg_packet *op)
 	  /* um... we didn't get the initial header */
 	  return(OV_EBADHEADER);
 	}
+        if(vc->vendor!=NULL){
+          /* previously initialized comment header */
+          return(OV_EBADHEADER);
+        }
 
 	return(_vorbis_unpack_comment(vc,&opb));
 
@@ -375,6 +378,14 @@ int vorbis_synthesis_headerin(vorbis_info *vi,vorbis_comment *vc,ogg_packet *op)
 	  /* um... we didn;t get the initial header or comments yet */
 	  return(OV_EBADHEADER);
 	}
+        if(vi->codec_setup==NULL){
+          /* improperly initialized vorbis_info */
+          return(OV_EFAULT);
+        }
+        if(((codec_setup_info *)vi->codec_setup)->books>0){
+          /* previously initialized setup header */
+          return(OV_EBADHEADER);
+        }
 
 	return(_vorbis_unpack_books(vi,&opb));