private int readNextByte() throws IOException {
    int read = mInputStream.read();
    mCurrentOffset++;
    if (read == -1) {
      throw new EOFException("Unexpected end of gif file");
    }
    return read;
  }
@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