Setting toggleChildrenVisibility to null also hides a line segment

```jsx
({
toggleChildrenVisibility: null,
})}
/>
```

I want to disable collapsing nodes (I want them always expanded). The closest I've been able to get that behaviour is by setting `toggleChildrenVisibility` to null, but this prevents the `rst__lineChildren` segment to be rendered, so you end up with a broken line coming down from the parent node. I think that segment should be outside the condition check for `toggleChildrenVisibility`.