Inconsistent Behavior in Nearly Degenerate Case

[LRenegar]

The following input errors for a SphericalPolygon, but not SingleSphericalPolygon:

points = np.array([[0.87772279707663836, 0.34018023965617028, 0.33746125116734926],
	[0.92276918091486326, 0.36291770695506587, 0.12956765310905877],
	[0.92574575323628161, 0.36907299235098134,-0.082340310189372115]])

Stack trace:

  File "<stdin>", line 1, in <module>
  File "/home/[USER_REDACTED]/anaconda3/lib/python3.7/site-packages/spherical_geometry/polygon.py", line 767, in __init__
    polygons.extend(g.disjoint_polygons())
  File "/home/[USER_REDACTED]/anaconda3/lib/python3.7/site-packages/spherical_geometry/graph.py", line 459, in disjoint_polygons
    self._sanity_check("disjoint - find all intersections")
  File "/home/[USER_REDACTED]/anaconda3/lib/python3.7/site-packages/spherical_geometry/graph.py", line 390, in _sanity_check
    assert len(node._edges) >= 2

[LRenegar]

To clarify, the following command produces the error:

import numpy as np
import spherical_geometry.polygon as polygon	   
points = np.array([[0.87772279707663836, 0.34018023965617028, 0.33746125116734926],
	[0.92276918091486326, 0.36291770695506587, 0.12956765310905877],
	[0.92574575323628161, 0.36907299235098134,-0.082340310189372115]])
	
p_valid = polygon.SingleSphericalPolygon(points)
p_error = polygon.SphericalPolygon(points)