fix: do not dispatch loadMore if hook is still in loading state

[jluyau]

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:

• in the S2 storybook, load the TableView > Test story
• note when switching between the All and A New Hope film filters, there's only one load call (logged in console as well)
• also note that when switching from All -> A New Hope, there's only 1 load called initially, and the second page call isnt made until scrolling down more (previous to this fix, the call would be made immediately)

🧢 Your Project:

[rspbot]

Build successful! 🎉

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• View the S2 docs

[rspbot]

Build successful! 🎉

• View the storybook
• View the S2 storybook
• View the documentation
• View the S2 docs