Minor grt fixes

- Fix the Classifier::saveBasesettingsToFile - if null rejection is enabled, the thresholds won't be saved and the load function fail because it expects those values. This change make it save the default (zero) values for the thresholds and fixes the problem.

- Remove an extra class declaration from MLBase::map function declaration (which is fine for gcc and I guess that it's ok for clang too, but it fails on Visual Studio).