private void flush_buf(OutputStream os, int len) throws Exception {
		os.write(len);
		os.write(bytes_buf,0,len);
		// Clear the bytes buffer
		bufIndex = 0;
		Arrays.fill(bytes_buf, 0, 0xff, (byte)0x00);
	}
This is intended to be called after writing all the frames if we write
an animated GIF frame by frame.

@param os OutputStream for the animated GIF
@throws Exception
subs/gif-revert/src/main/java/com/engineer/gif/revert/lib/AnimatedGIFWriter.java