VideoCapture MSMF plugin won't open using camera/device index.

[pdy]

System Information

OpenCV version: at least from 4.5.5 to master
Operating System / Platform: Windows 10/11
Compiler & compiler version: Visual Studio 2022

Detailed description

It looks like unnecessary nullptr check of optional argument https://github.com/opencv/opencv/blob/4.8.0/modules/videoio/src/cap_msmf.cpp#L2722
Below linked fragment with my comments. By commenting out pointed filename check I was able to open camera on my local machine.

static
CvResult CV_API_CALL cv_capture_open_with_params(
    const char* filename, int camera_index,
    int* params, unsigned n_params,
    CV_OUT CvPluginCapture* handle
)
{
    if (!handle)
        return CV_ERROR_FAIL;
    *handle = NULL;
    if (!filename)                           // <--- filename is optional, see below
        return CV_ERROR_FAIL;      
    CaptureT* cap = 0;
    try
    {
        cv::VideoCaptureParameters parameters(params, n_params);
        cap = new CaptureT();
        bool res;
        if (filename)                                                    // if filename is true then we use
            res = cap->open(std::string(filename), &parameters);         //
        else                                                             // however if it's nullptr
            res = cap->open(camera_index, &parameters);                  // then we use index to search device
        if (res)
        {
            *handle = (CvPluginCapture)cap;
            return CV_ERROR_OK;
        }
    }
    catch (const std::exception& e)
    {
        CV_LOG_WARNING(NULL, "MSMF: Exception is raised: " << e.what());
    }
    catch (...)
    {
        CV_LOG_WARNING(NULL, "MSMF: Unknown C++ exception is raised");
    }
    if (cap)
        delete cap;
    return CV_ERROR_FAIL;
}

Steps to reproduce

Open video capture from camera (for example, laptop's built-in camera) using MSMF backend cv::VideoCapture vc(0, cv::CAP_MSMF); built as a plugin.

It's also very likely, that it's the same issue as #23056

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues, forum.opencv.org, Stack Overflow, etc and have not found any solution
• I updated to the latest OpenCV version and the issue is still there
• There is reproducer code and related data files (videos, images, onnx, etc)