Fix SelectAll logic for falsy keys

[snowystinger]

Closes

Found while testing https://github.com/adobe/react-spectrum/pull/6631 where selecting the first item in the Virtualized Table would cause the select all checkmark to render checked instead of indeterminate

✅ 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:

🧢 Your Project:

[rspbot]

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[rspbot]

Build successful! 🎉

• View the storybook
• View the storybook-19
• View the storybook-17
• View the storybook-16
• View the documentation

[rspbot]

## API Changes

unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any', access: 'private' } unknown top level export { type: 'any', access: 'private' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'identifier', name: 'Column' } unknown top level export { type: 'identifier', name: 'Column' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown type { type: 'link' } unknown type { type: 'link' } unknown type { type: 'link' } unknown type { type: 'link' } unknown type { type: 'link' } unknown type { type: 'link' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' } unknown top level export { type: 'any' }