private void readNetscapeExtension() throws IOException {
    int size;
    do {
      size = readBlock();
      if (block[0] == 1) {
        mLoopCount = ((((int) block[2]) & 0xff) << 8) | (((int) block[1]) & 0xff);
      }
    } 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