In the method Segment() index1 needs to be checked as well as index2 in Geom_BSplineSurface and Geom2d_BSplineCurve
(Geom_BSplineCurve already has this check).
New test cases bug31402_1, bug31402_2 has been added.
The unnecessary code block in Geom2d_BSplineCurve has been deleted,
and checking index2 block has beed extended.
