Fix rare issue where video stream sample indices would be determined incorrectly, breaking video inspection UI & playback

[Wumpf]

This is fairly difficult to hit in the wild, but would happen when receiving chunks that for some reason either:

• have unused extra data in their video sample component array
• have video sample components that are used only on some arrays

I've hit this on on my ongoing chunk cropping PR because at the moment the cropping doesn't necessarily discard underlying sample data, causing previously unexpected array offsets.

[github-actions]

Web viewer built successfully.

Result	Commit	Link	Manifest
✅	b937ecb	https://rerun.io/viewer/pr/11308	+nightly +main

^{Note: This comment is updated whenever you push a commit.}