ProbabilisticClassificationModel.normalizeToProbabilitiesInPlace should return probabilities when given all-0 vector

ProbabilisticClassificationModel.normalizeToProbabilitiesInPlace returns a vector of all-0 when given a rawPrediction vector of all-0. It should return a valid probability vector with the uniform distribution.

Note: This will be a behavior change but it should be very minor and affect few if any users. But we should note it in release notes.