Navigation bar elements flickering

[evil159]

Describe the bug

Some navigation bar elements(UIBarButtonItems and UINavigationitems with custom views) flicker when navigation bar gets hidden interactively.

To Reproduce

The issues manifests quite easily, for example when setting up an item with custom image view:

    let imageView = UIImageView(image: UIImage(named: "AppIcon"))
    navigationItem.rightBarButtonItem = UIBarButtonItem(customView: imageView)

or event just an empty view

    let titleView = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 30))
    titleView.backgroundColor = .white
    navigationItem.titleView = titleView

Here's a sample project that demonstrates this:
Sample.zip

Expected behavior
Would be nice if it wouldn't flicker.

[evil159]

Related issues - #325, #257.