Merge pull request #26587 from anandkaranubc:fix-nu-svc-parameter-check

Fix #25812: Add error handling for invalid nu parameter in SVM NU_SVC #26587

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work [Issue #25812](https://github.com/opencv/opencv/issues/25812)
- [ ] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake

modules/ml/src/svm.cpp

@@ -41,10 +41,12 @@
 //M*/
 
 #include "precomp.hpp"
+#include <opencv2/core/utils/logger.hpp>
 
 #include <stdarg.h>
 #include <ctype.h>
 
+
 /****************************************************************************************\
                                 COPYRIGHT NOTICE
                                 ----------------
@@ -1458,9 +1460,10 @@ public:
                     for( j = i+1; j< class_count; j++ )
                     {
                         int cj = class_ranges[j+1] - class_ranges[j];
-                        if( nu*(ci + cj)*0.5 > std::min( ci, cj ) )
-                            // TODO: add some diagnostic
+                        if( nu*(ci + cj)*0.5 > std::min( ci, cj ) ) {
+                            CV_LOG_ERROR(NULL, "Training cases incompatible with nu parameter—try a lower value.");
                             return false;
+                        }
                     }
                 }
             }