prevent ZeroDivision caused by parallel lines

git-svn-id: https://pycam.svn.sourceforge.net/svnroot/pycam/trunk@514 bbaffbd6-741e-11dd-a85d-61de82d9cad9

src/pycam/Geometry/Model.py

@@ -258,7 +258,11 @@ class ContourModel(BaseModel):
             b = x4.sub(x3)
             c = x3.sub(x1)
             # see http://mathworld.wolfram.com/Line-LineIntersection.html (24)
+            try:
                 factor = c.cross(b).dot(a.cross(b)) / a.cross(b).normsq()
+            except ZeroDivisionError:
+                l2.p1 = None
+                return
             if not (0 <= factor < 1):
                 # The intersection is always supposed to be within p1 and p2.
                 l2.p1 = None