Fix ComposeAccessibleComponent.getAccessibleChild

[m-sasha]

ComposeAccessibleComponent.getAccessibleChild was trying to incorrectly access auxiliaryChildren if controller.accessibleByNodeId returned null.

Fixes JetBrains/compose-multiplatform#4778

Testing

1. Run the code below
2. Turn on VoiceOver
3. Scroll the list with the mouse wheel.
4. Press tab.

fun main() {
    application {
        Window(
            onCloseRequest = ::exitApplication
        ) {
            LazyColumn {
                items(100) {
                    Text("Item $it")
                }
            }
        }
    }
}

Note that this doesn't reproduce in latest jb-main, probably due to focus traversal changes.

[MatkovIvan]

I'd love to see unit tests for this case to prevent regressions

[m-sasha]

I'd love to see unit tests for this case to prevent regressions

It's a silly mistake that's not likely to be repeated, and it's hard to set up a test for this. I don't think it's worth it.