private void skipExtension() throws IOException {
    int size;
    do {
      size = readBlock();
    } while (size > 0);
  }
@param is InputStream to decode
@param os OutputStream to write fixed version of gif, if needed. (optional)
animated-gif-lite/src/main/java/com/facebook/animated/giflite/decoder/GifMetadataDecoder.java