Certain paths cause crashes

This is less clear-cut than #24, but I'm still getting crashes with some fairly benign-looking patterns:

poly_point_isect.isect_polygon([[0. , 0. ],
           [1. , 0. ],
           [0. , 1. ],
           [0. , 0. ],
           [0.5, 0. ],
           [1. , 1. ]])  # crashes

The following crash when using np.float32 arithmetic but are fine using np.float64 or simply float:

poly_point_isect.isect_polygon(np.array([
           [0.    , 0.    ],
           [0.5   , 0.    ],
           [1.    , 0.1163]], dtype=np.float32))  # crashes

poly_point_isect.isect_polygon(np.array([[1, 0], [0.27344, 0], [0, 0.17]], dtype=np.float32))  # crashes

[nosy-b]

Same :)