[Visualizer] Fix crashes and exceptions in updatePointCloud()

[larshg]

Setting the Cells count more explicitly seems to do the trick.

vertices->SetCells (nr_points, cells);

Failed to correctly identify that we changed its array/count. Maybe, one should look into this another day,

Closes #3452

[kunaltyagi]

Perhaps merge the test with the code. And if it fixes the test, looks like you get 1 week worth of beer (or the drink of your choice)

[larshg]

I just added them in seperate PRs. so we can see it actually fail now, before the fix gets merged.

[kunaltyagi]

Please keep in mind that merging a failing test into master makes little sense.

If the CI fails there, that'd confirm that the test is correct. After that, please consider moving those tests here and we'll merge once the CI turns green.

[kunaltyagi]

LGTM.

Let's also close #4016 in favor of another issue/PR to track the issue of the tests not being compiled/run?

[kunaltyagi]

CI is green.

@larshg Please squash to have only 2 commits (test + mitigation). Ping someone after that so we can merge it.

[kunaltyagi]

Merging because no content changed, and CI was green before