Merge pull request #27353 from MRo47:fix/segfault-on-forward#27352

Fix #27352: Add checks before getting latest pin in Net::Impl::getLatestLayerPin() #27353 

### Pull Request Readiness Checklist

Fixes #27352 

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/dnn/src/net_impl.cpp

@@ -1027,6 +1027,8 @@ void Net::Impl::forward(OutputArrayOfArrays outputBlobs,
         const std::vector<String>& outBlobNames)
 {
     CV_Assert(!empty());
+    if (outBlobNames.empty())
+        CV_Error(Error::StsBadArg, "in Net::forward(), outBlobNames cannot be empty");
     FPDenormalsIgnoreHintScope fp_denormals_ignore_scope;
 
     std::vector<LayerPin> pins;
@@ -1056,6 +1058,8 @@ void Net::Impl::forward(std::vector<std::vector<Mat>>& outputBlobs,
         const std::vector<String>& outBlobNames)
 {
     CV_Assert(!empty());
+    if (outBlobNames.empty())
+        CV_Error(Error::StsBadArg, "in Net::forward(), outBlobNames cannot be empty");
     FPDenormalsIgnoreHintScope fp_denormals_ignore_scope;
 
     std::vector<LayerPin> pins;
@@ -1316,6 +1320,9 @@ void Net::Impl::updateLayersShapes()
 
 LayerPin Net::Impl::getLatestLayerPin(const std::vector<LayerPin>& pins) const
 {
+    if (pins.empty())
+        CV_Error(Error::StsBadArg,
+                 "Cannot Net::Impl::getLatestLayerPin() from empty vector of pins");
     return *std::max_element(pins.begin(), pins.end());
 }