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

• [x] Bug fix (non-breaking change which fixes an issue): Fixes #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:

• [x] I have run python util/check_style.py --apply to apply Open3D code style to my code.
• [x] 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.
• [x] I will follow up and update the code if CI fails.
• [x] 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.

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