iOS videoview doesn't display.

## 🐛 Bug Report
Same situation as #589 but in iOS. Video fails to display at all. Source loads, notification controls work and sound plays, but no video or controls on screen.

### Output
2019-08-12 12:59:06.243 ChatUIXForms.iOS[338:15167] VideoPlayer [INFO]: Initializing Xamarin Forms Video Player on iPhone v12.4
2019-08-12 13:00:09.836 ChatUIXForms.iOS[338:15167] -[AVAsset loadValuesAsynchronouslyForKeys:completionHandler:] invoked with unrecognized keys (
albumName,
author,
title,
artist
).

**Version:** 0.8.6

**Platform:**
- [x] :iphone: iOS 12.4 real iPhone 8
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [ ] :apple: MacOS
- [ ] :tv: tvOS
- [x] :monkey: Xamarin.Forms

Start by reproducing the issue on an iPhone 8 running iOS 12.4 with Xamarin.Forms and compare the behavior with issue #589. Check the AVAsset warning in the supplied output; done means video and on-screen controls display while source loading, notification controls, and sound continue to work.

Written by the indexing model from the issue text.