FIX SelectPercentile limit bug

SelectPercentile had a tie breaker mechanism that just took the first `percentile / 100. * len(features)` selected features. So if scores were `[0, 0, 1]`, selecting the top third would mask `[F F T]`, but the top two-thirds would mask `[T F F]`, i.e. missing the best score entirely.

This is a fix.