Merge pull request #25981 from Kumataro:fix25971

imgproc: add specific error code when cvtColor is used on an image with an invalid number of channels #25981

close #25971

### 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
- [x] 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/core/src/check.cpp

@@ -155,7 +155,12 @@ void check_failed_MatType(const int v, const CheckContext& ctx)
 }
 void check_failed_MatChannels(const int v, const CheckContext& ctx)
 {
-    check_failed_auto_<int>(v, ctx);
+    std::stringstream ss;
+    ss  << ctx.message << ":" << std::endl
+        << "    '" << ctx.p2_str << "'" << std::endl
+        << "where" << std::endl
+        << "    '" << ctx.p1_str << "' is " << v;
+    cv::error(cv::Error::BadNumChannels, ss.str(), ctx.func, ctx.file, ctx.line);
 }
 void check_failed_true(const bool v, const CheckContext& ctx)
 {