Add detection for Ogg skeleton metadata

stb_vorbis.c

@@ -374,7 +374,8 @@ enum STBVorbisError
    VORBIS_invalid_first_page,
    VORBIS_bad_packet_type,
    VORBIS_cant_find_last_page,
-   VORBIS_seek_failed
+   VORBIS_seek_failed,
+   VORBIS_ogg_skeleton_not_supported
 };
 
 
@@ -3579,6 +3580,18 @@ static int start_decoder(vorb *f)
    // check for expected packet length
    if (f->segment_count != 1)                       return error(f, VORBIS_invalid_first_page);
    if (f->segments[0] != 30)                        return error(f, VORBIS_invalid_first_page);
+      // check for the Ogg skeleton fishead identifying header to refine our error
+      if (f->segments[0] == 64 &&
+          getn(f, header, 6) &&
+          header[0] == 'f' &&
+          header[1] == 'i' &&
+          header[2] == 's' &&
+          header[3] == 'h' &&
+          header[4] == 'e' &&
+          header[5] == 'a' &&
+          get8(f)   == 'd')                         return error(f, VORBIS_ogg_skeleton_not_supported);
+      else
+                                                    return error(f, VORBIS_invalid_first_page);
    // read packet
    // check packet header
    if (get8(f) != VORBIS_packet_id)                 return error(f, VORBIS_invalid_first_page);