Workaround for bug when observing optionals with KVO

[tkrajacic]

app-architecture/Recordings-MVVM-C-less-rx/Recordings/PlayViewController.swift

Lines 6 to 8 in ee561c7

	// TODO: change.newValue should never be `nil`, but when observing an optional property that's set to `nil`, then change.newValue is `nil` instead of `Optional(nil)`. This is the bug report for this: https://bugs.swift.org/browse/SR-6066
	guard let newValue = change.newValue else { return }
	onChange(newValue)

This can be worked around with some funny casting:

let newValue = change.newValue ?? (nil as Any? as! Value)
onChange(newValue)

Then we can also observe optionals correctly.

Thanks to the awesome help of Jordan Rose of the Swift team for providing the workaround!