title: Toggling IsVisible for an stacklayout inside scrollview does not update properly in Xamarin forms iOS
body: <p>I am having lot of <strong>stacklayout</strong> views inside scrollview, and the stacklayouts visibility property set to "true" or "false" based on the option selected. Making stacklayout isvisible property to "true" is not working in <strong>Xamarin Forms 1.4.0</strong> and instead of showing the stacklayout view it's just showing empty space between the views.but it was working fine in <strong>Xamarin Forms 1.3.3</strong>. happening only in iOS, in android it is working as expected. </p>
  
  <p>Any help would be much appreciated.</p>