Merge pull request #23766 from TolyaTalamanov:at/segmentation-demo-desync

G-API: Refine Semantic Segmentation Demo #23766

### Overview
* Supported demo working with camera id (e.g `--input=0`)
* Supported 3d output segmentation models (e.g `deeplabv3`)
* Supported `desync` execution
* Supported higher camera resolution
* Changed the color map to pascal voc (https://cloud.githubusercontent.com/assets/4503207/17803328/1006ca80-65f6-11e6-9ff6-36b7ef5b9ac6.png)

### Pull Request Readiness Checklist

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

- [ ] I agree to contribute to the project under Apache 2 License.
- [ ] 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
- [ ] The PR is proposed to the proper branch
- [ ] 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/python/src2/cv2_convert.hpp

@@ -268,6 +268,11 @@ PyObject* pyopencv_from(const std::vector<Tp>& value)
 template<typename K, typename V>
 bool pyopencv_to(PyObject *obj, std::map<K,V> &map, const ArgInfo& info)
 {
+    if (!obj || obj == Py_None)
+    {
+        return true;
+    }
+
     PyObject* py_key = nullptr;
     PyObject* py_value = nullptr;
     Py_ssize_t pos = 0;