fix(tilegroup): guard usage of potentially null children properties

[tay1orjones]

Surfaced in slack

When conditionally rendering RadioTiles within a TileGroup a race condition existed where children properties (child.type, child.props.children) could be null and would throw an uncaught exception.

Original repro: https://stackblitz.com/edit/github-mgvclx?file=src%2FExample%2FExample.jsx

Changelog

New

• Add a test to cover this race condition

Changed

• Use optional chaining on child property assertions

Testing / Reviewing

• You can recreate the repro locally to validate it'll work, but the new test covers it as well and should pass.

[guidari]

LGTM!! 🚀

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