Merge pull request #4 from kemnitzs/master

small fix to make this work with opencv-3.4.1 under centos8 newest ub…

src/aux-level/train-aux.cpp

@@ -44,7 +44,7 @@ Ptr<StatModel> train_svm(Ptr<TrainData> TrainData, par_train_t *train, FILE *fp)
     svm->setType(SVM::C_SVC);
   } else {
     printf("unknown SVM method\n");
-    return NULL;
+    exit(FAILURE);
   }
 
   svm->setKernel(SVM::RBF);