Merge pull request #28404 from NechamaKrashinski:imgproc-cornersubpix-error-handling

imgproc: replace assertion in cornerSubPix with descriptive error #28404

Replace CV_Assert with explicit bounds check for initial corners in cornerSubPix.

This provides a descriptive runtime error instead of abrupt termination,
improving error handling for Python and C++ users.

No algorithmic or behavioral change for valid inputs.

Fixes #25139 (Related to #7276).

### 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
- [ ] 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/imgproc/src/cornersubpix.cpp

@@ -96,7 +96,11 @@ void cv::cornerSubPix( InputArray _image, InputOutputArray _corners,
     for( int pt_i = 0; pt_i < count; pt_i++ )
     {
         Point2f cT = corners[pt_i], cI = cT;
-        CV_Assert( Rect(0, 0, src.cols, src.rows).contains(cT) );
+        if (!Rect(0, 0, src.cols, src.rows).contains(cT))
+        {
+            CV_Error(Error::StsOutOfRange,
+                    "cornerSubPix: initial corner is outside the image.");
+        }
         int iter = 0;
         double err = 0;