Fix the visualization of boxes.

[S-Dafarra]

This fixes a bug in the visualization of boxes introduced by #845

The reason why that change was added in the first place was because I tried to add a box in the visualizer. In particular, I used a code like

    iDynTree::Box box;

    box.setX(0.1);
    box.setY(0.2);
    box.setZ(1.0);
    addGeometryToSceneManager(&box, nullptr, pimpl->m_irrSmgr);

I was expecting a box much bigger on the Z axis, but it was not the case. Indeed, it turned out that the orientation of the box was variable. Finally, by checking with valgrind, I realized that link_H_geometry was read when adding the mesh to the visualizer, but it was never set. Adding the initialization of link_H_geometry solved the problem for valgrind and in the visualization.

[S-Dafarra]

This problem was originally discovered by @lrapetti after using the Human URDF

[lrapetti]

Thanks for the fix.

Here it is the output of idyntree-model-view with the current master (with human-gazebo model)

Here it is after @S-Dafarra changes