iOS: Still buffering after Stop()

## 🔙 Regression

I fixed this in https://github.com/Baseflow/XamarinMediaManager/pull/774

### Old (and correct) behavior

No data consumed after stop.

### Current behavior

Data consumed after stop.

### Reproduction steps

See here: https://github.com/Baseflow/XamarinMediaManager/issues/773

### Configuration

**Version:** 1.0.8

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

Start by reviewing issue 773 and pull request 774, which are the stated reproduction and prior fix references. Compare the old and current Stop behavior on iOS and macOS; done means no data is consumed after Stop().

Written by the indexing model from the issue text.