Fix overconstrained triangles treatment in create_mesh

The problem was that SMESH is marking as borders not only free borders but also edges of zones defined in geometry (refinement zones for example). So, the correction for overconstrained triangles which consist into inverting diagonal of the element overscontrained was applying on element in the middle of the mesh and not only those on free borders. Hence, the resulting mesh was invalid for TELEMAC.

The original treatment was working in Salome 9.7 but no longer in recent versions of Salome. This fix has been tested with 9.10 and 9.11.