fix: points.size is not a function at PointCloudViewer.addPointCloud

[luoxuhai]

Description of change

Pre-Merge Checklist

• [x] Tests and/or benchmarks are included
• [x] Documentation is changed or added
• [x] Lint process passed (npm run lint)
• [x] Tests passed (npm run test)

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Name	Status	Preview	Updated
pcl-js	✅ Ready (Inspect)	Visit Preview	Sep 29, 2022 at 3:02PM (UTC)