iOS UIDatePicker in UIDatePickerMode.countDownTimer value changed bug

## ViewController.swift
import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        // Create a DatePicker
        let datePicker: UIDatePicker = UIDatePicker()

        // Posiiton date picket within a view
        datePicker.frame = CGRect(x: 10, y: 50, width: self.view.frame.width, height: 200)

        // Set some of UIDatePicker properties
        datePicker.backgroundColor = UIColor.white
        datePicker.datePickerMode = UIDatePickerMode.countDownTimer;

        // Add an event to call onDidChangeDate function when value is changed.
        datePicker.addTarget(self, action: #selector(ViewController.datePickerValueChanged(_:)), for: .valueChanged)

        // Add DataPicker to the view
        self.view.addSubview(datePicker)

    }

    // Not called the first time
    func datePickerValueChanged(_ sender: UIDatePicker){
        print("Selected value \(sender.countDownDuration)")
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}