random unwrap issue

[looooo]

Running the Python command 'PatternCommand' failed:
Traceback (most recent call last):
  File "/home/lo/projects/openglider/OpenGlider/freecad/freecad_glider/tools/__init__.py", line 167, in Activated
    pat.unwrap(file_name, obj.Proxy.getGliderInstance())
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/patterns.py", line 153, in unwrap
    super().unwrap(outdir)
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/patterns.py", line 108, in unwrap
    all_patterns = self._get_plotfile()
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/patterns.py", line 89, in _get_plotfile
    plots.unwrap()
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/glider/__init__.py", line 164, in unwrap
    self.get_ribs()
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/glider/__init__.py", line 83, in get_ribs
    rib_plot.flatten(self.glider_3d)
  File "/home/lo/projects/openglider/OpenGlider/openglider/plots/glider/ribs.py", line 43, in flatten
    self.outer = self.inner.copy().add_stuff(self.config.allowance_general)
  File "/home/lo/projects/openglider/OpenGlider/openglider/vector/polyline.py", line 355, in add_stuff
    newlist.append(second + self.normvectors[i] * amount / cosphi)
  File "/home/lo/projects/openglider/OpenGlider/openglider/utils/cache.py", line 60, in __get__
    res = self.function(parentclass)
  File "/home/lo/projects/openglider/OpenGlider/openglider/vector/polyline.py", line 283, in normvectors
    rotate(self.data[j + 1] - self.data[j - 1]))
  File "/home/lo/projects/openglider/OpenGlider/openglider/vector/polyline.py", line 278, in <lambda>
    rotate = lambda x: normalize(x).dot([[0, -1], [1, 0]])
  File "/home/lo/projects/openglider/OpenGlider/openglider/vector/functions.py", line 26, in normalize
    raise ValueError("Cannot normalize a vector of length Zero")