Fix useDateSegment null ref error #6988

[teemuandersen]

Closes

✅ Pull Request Checklist:

• Included link to corresponding React Spectrum GitHub Issue.
• Added/updated unit tests and storybook for this change (for new code or code which already has tests).
• Filled out test instructions.
• Updated documentation (if it already exists for this component).
• Looked at the Accessibility Practices for this feature - Aria Practices

📝 Test Instructions:

It is kinda hard to reproduce the issue, but can't figure out how this null check could do any harm.

[snowystinger]

Thanks for the PR, you'll need to sign the CLA https://react-spectrum.adobe.com/contribute.html#contributor-license-agreement
Then you may need to close and reopen the PR to get it to take hold.