Fix DynamicPreferenceCombiner returning early

[jcmosc]

An item in a dynamic container may be missing a preference if, say, it does not return a display list:

struct MyEmptyView: View, PrimitiveView, UnaryView {
    func _makeView(view: _GraphValue<Self>, inputs: _ViewInputs) -> _ViewOutputs {
        _ViewOutputs()
    }
}

Spacer is an example of this.

When such a view is placed in a dynamic list such as a ForEach, any subsequent views fail to render because their display lists are never combined.

[Kyle-Ye]

Thanks. Would you mind adding a ui test in Example/OpenSwiftUIUITests to cover the fix?

[Kyle-Ye]

augment review

[augmentcode]

Sorry, Augment does not have access to the org this pull request's branch is from.

[Kyle-Ye]

The current fix solve some case but still have issue for other case.

eg.

struct ContentView: View {
    var body: some View {
        VStack {
            Color.red
            Color.green
            ForEach(0 ..< 1) { index in
                Spacer()
                Color.blue
            }
        }
    }
}