Report: Combobox crashes with empty option groups

Repro

1. Pass an option group with an empty options array
2. Open the Combobox
3. Crash on first keystroke

TypeError: Cannot read properties of undefined (reading 'value')
   at getFirstOption (combobox.tsx:88)
   at handleKeyDown (combobox.tsx:203)

Reported through the docs feedback widget. Needs triage: either skip empty groups at render time or guard getFirstOption.