Merge pull request #24101 from LaurentBerger:I24076

Invalid memory access fix for ONNX split layer parser #24076 #24101

### 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 https://github.com/opencv/opencv/issues/24076
- [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.
- [x] The feature is well documented and sample code can be built with the project CMake

modules/dnn/src/onnx/onnx_importer.cpp

@@ -1385,7 +1385,12 @@ void ONNXImporter::parseSplit(LayerParams& layerParams, const opencv_onnx::NodeP
         CV_Assert(constBlobs.find(node_proto.input(1)) != constBlobs.end());
         Mat splitsBlob = getBlob(node_proto, 1);
         int splitSize = splitsBlob.total();
-
+        if (splitSize == 1)
+        {
+            layerParams.set("num_split", 1);
+        }
+        else
+        {
             std::vector<int> slicePoints(splitSize - 1, splitsBlob.at<int>(0));
             for (int i = 1; i < splitSize - 1; ++i)
             {
@@ -1393,6 +1398,7 @@ void ONNXImporter::parseSplit(LayerParams& layerParams, const opencv_onnx::NodeP
             }
             layerParams.set("slice_point", DictValue::arrayInt(&slicePoints[0], slicePoints.size()));
         }
+    }
     else
     {
         layerParams.set("num_split", node_proto.output_size());