Reading group node information triggers DOMWidget callbacks (TRIVIAL FIX INCLUDED)

If you call `getInnerNodes()` on a group node, it calls `updateInnerWidgets` (groupNode.js:685).

`updateInnerWidgets` at line 1032-1034 then reads

```javascript
if (widget) {
widget.value = newValue;
}
```

Which is innocent enough, except that for DOMWidgets setting value triggers an optional callback, which you wouldn't expect to happen when a *get* method is called.

Two possible fixes:
- move line 685 inside the `if` starting at 674, or
- modify 1032 to read `if (widget && widget.value != newValue) {`

Start in groupNode.js at the getInnerNodes call around line 685 and inspect updateInnerWidgets around lines 1032-1034. Confirm that reading group-node information no longer triggers a DOMWidget value callback, and verify the existing group-node behavior remains unchanged.

Written by the indexing model from the issue text.