message: Prevent crash when attempting to create training data without responses.
  This is at least useful when using an SVM one-class linear classifier, so there are valid use cases.
diff: @@ -403,7 +403,7 @@ public:
  Mat(tempCatMap).copyTo(catMap);
  }
  - if( varType.at<uchar>(ninputvars) == VAR_CATEGORICAL )
  + if( noutputvars > 0 && varType.at<uchar>(ninputvars) == VAR_CATEGORICAL )
  {
  preprocessCategorical(responses, &normCatResponses, labels, &counters, sortbuf);
  Mat(labels).copyTo(classLabels);
  