class_labels of SVM::trainAuto is not consistent with that of SVM::train (Bug #4464)

To fix Bug #4030, in SVM.cpp Line 1672

Mat class_labels0 = class_labels;

class_labels = class_labels0;

However, as a result, class_labels in the model trained by SVM::trainAuto are converted to int ranging from 0...class_count-1. But in SVM::train, the class_labels would be the original class_labels.

Actually, I find these two lines are necessary. The real problem is that when Mat class_labels0 = class_labels; class_labels has no value. The value is assigned by class_labels = data->getClassLabels(); in the latter if-statement.

So after

// temporarily replace class labels with 0, 1, ..., NCLASSES-1
Mat(temp_class_labels).copyTo(class_labels);

class_labels0 does not preserve the orignial class_labels. Finally before the return statement, class_labels = class_labels0;, now class_labels is lost.

My solution is to add class_labels.copyTo(class_labels0); before Mat(temp_class_labels).copyTo(class_labels);