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Issue description:
https://forum.freecad.org/viewtopic.php?f=3&t=70325https://github.com/FreeCAD/FreeCAD/issues/7520
The general algorithm to calculate normals miserably fails when
the curve is a line segment and the point through which the normal
to a curve is to be drawn is colinear with the line segment.
The solution is to provide specific code for this corner case.
fixes#7520
4b5a796a67