Fix divison zero in ComputeMaxIterations
Fix divison zero in ComputeMaxIterations

when inlier ratio is really low, log_prob becomes zero eventually returning 1 as NumberOfMaxIterations.
As a result, Ransac/Prosac would terminate too early with very low confidence

Change-Id: Ie528bc97f47f29f06ecd2e9e7a6963ba42e6ae33

zhanshenman/TheiaSfM,zhanshenman/TheiaSfM,zhanshenman/TheiaSfM,zhanshenman/TheiaSfM,zhanshenman/TheiaSfM