Another group node failure

Here's another JS failure related to group nodes:

```
Uncaught (in promise) TypeError: Cannot read properties of undefined (reading '0')
at GroupNodeHandler.updateInnerWidgets (groupNode.js:929:63)
at GroupNodeHandler.node.getInnerNodes (groupNode.js:674:9)
at ComfyApp.graphToPrompt (app.js:1695:59)
at ComfyApp.queuePrompt (app.js:1859:27)
at HTMLButtonElement.onclick (ui.js:626:24)
```

I don't have a reproducible example yet, but maybe the stacktrace already tells you something!

cc @pythongosssss