Unable to parse camera parameters with vpXmlParserCamera::parse() when camera name is empty

[rolalaro]

Issue

When calling vpXmlParserCamera::parse without specifying the camera name, the parsing does not work even if there is only one camera in the file.

Expected behavior

According to the documentation, if the XML file contains only one camera, the parsing should succeed.

To reproduce the error

#include <visp3/core/vpIoTools.h>
#include <visp3/core/vpXmlParserCamera.h>

int main() {
    // Get the user login name
    std::string username;
    vpIoTools::getUserName(username);

    std::string tmp_dir += username + "/test_xml_parser_camera/";
    vpIoTools::remove(tmp_dir);
    std::cout << "Create: " << tmp_dir << std::endl;
    vpIoTools::makeDirectory(tmp_dir);

    // Create the camera model
    vpCameraParameters cam;
    std::vector<double> distortion_coeffs;
    distortion_coeffs.push_back(-0.00297341705299914);
    distortion_coeffs.push_back(0.0352853797376156);
    distortion_coeffs.push_back(-0.032205019146204);
    distortion_coeffs.push_back(0.004446716979146);
    distortion_coeffs.push_back(0);
    cam.initProjWithKannalaBrandtDistortion(285.523895263672, 286.6708984375, 420.874114990234, 381.085388183594, distortion_coeffs);

    // Save the model in a file
    std::string filename = tmp_dir + "test_write_cam_with_KannalaBrandt_distortion.xml";
    {
      vpXmlParserCamera xml;
      std::cout << "Write to: " << filename << std::endl;
      if (xml.save(cam, filename, "Camera", 800, 848) != vpXmlParserCamera::SEQUENCE_OK) {
        std::cerr << "Cannot save XML file: " << filename << std::endl;
        return EXIT_FAILURE;
      }
    }

    vpCameraParameters cam_read;
    {
      vpXmlParserCamera xml;
      xml.parse(cam_read, filename, "", vpCameraParameters::ProjWithKannalaBrandtDistortion, 800, 848, false);
      std::cout << "Cam write:\n" << cam << std::endl;
      std::cout << "Cam read:\n" << cam_read << std::endl;
      if (cam != cam_read) {
        std::cerr << "Issue when parsing XML file: " << filename << std::endl;
        return EXIT_FAILURE;
      }
    }
    return EXIT_SUCCESS;
}

[rolalaro]

Proposed a PR (#1297) to solve the issue