fix failure of non-regression test SMESH_TEST/Grids/smesh/mesh_Projection_2D/A1

fix failure of non-regression test SMESH_TEST/Grids/smesh/mesh_Projection_2D/A1

 Avoid returning EDGE position for 2 nodes on the same EDGE, while the
 medium node should be on FACE. The case is a triangle whose 3 nodes are on
 the same EDGE. The worst is that in this case the medium node which
 is logically on FACE falls to a straight EDGE, as the triangle is of
 zero area (thanks to MEFISTO)

 std::pair<int, TopAbs_ShapeEnum> GetMediumPos(const SMDS_MeshNode* n1,
                                               const SMDS_MeshNode* n2,
+                                              const bool           useCurSubShape=false);