0024595: STEP import missing surfaces

0024595: STEP import missing surfaces

Modification to create natural bounds for face based on the spherical and Bspline surface and having only one bound represented by Vertex loop was made.
 According to the specification of ISO-10303 part 42:
    "If the face has only one bound and this is of type vertex_loop, then the interior of the face is the domain of the face_surface.face_geometry. In such a case the underlying surface shall be closed (e.g. a spherical_surface.)"
    - natural bounds are applied only in case if VertexLoop is only the one
      defined face bound.