title: mpvolumeview on rotation doesn't take touch properly
body: <p>I am using a mpvolumeview in vertical position in my app. But now I am not able to slide in slider properly. It only works at the bottom of slider.</p>
  
  <p>My code for adding MPVolumeView:</p>
  
  <pre><code>volumeViewVertical = MPVolumeView(frame: CGRect(x: 60, y: -80, width: 140, height: 140))
      volumeViewVertical.backgroundColor = .yellow
      volumeViewVertical.setVolumeThumbImage(UIImage(named: "vc_slider_circle"), for: .normal)
      volumeViewVertical.volumeSlider.minimumTrackTintColor = UIColor.white
      volumeViewVertical.showsRouteButton = false
      volumeViewVertical.transform = CGAffineTransform(rotationAngle: -CGFloat(M_PI_2))
      sliderLayoutViewVertical?.addSubview(volumeViewVertical)
  </code></pre>
  
  <p>Regards</p>