Fix ransac update of the iteration number

[nicolaloi]

The update of the iteration number is forced to be non-negative (was negative if corres_inlier_ratio = 0.0)

Type

• Bug fix (non-breaking change which fixes an issue): Fixes RANSAC exits early when no checker is passed #6709
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Issue 6709: RANSAC incorrectly exits early if corres_inlier_ratio is 0.0 during a RANSAC iteration.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

The corres_inlier_ratio of a specific RANSAC iteration is employed to update est_k_local_d (the maximum number of iterations to be performed) using the formula $est\_k\_local\_d={\text{log} (1-criteria.confidence\_ ) \over \text{log} ( 1-corres\_inlier\_ratio^{ransac\_n})}$.

However, if corres_inlier_ratio = 0.0 then est_k_local_d = -inf. Hence, the maximum number of iterations is negative and RANSAC exits early.

Instead, we want RANSAC to continue to test new transformations. This PR adds a check to ensure that est_k_local_d is non-negative.

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[ssheorey]

THanks @nicolaloi ! Looks good.