fix intersection ValueError

checks if intersection_segment_plane returns the mesh vertex (u or v of the edge ). 
if True appends the mesh vertex itself to intersections instead of calculating t. otherwise when mesh.split_edge is executed, it raises ValueError: t should be greater than 0.0. or ValueError: t should be smaller than 1.0.

Author: nizartaha

src/compas/datastructures/mesh/slice.py

@@ -146,11 +146,16 @@ def intersect(self):
             x = intersection_segment_plane((a, b), self.plane)
             if not x:
                 continue
-            L_ax = length_vector(subtract_vectors(x, a))
-            L_ab = length_vector(subtract_vectors(b, a))
-            t = L_ax / L_ab
-            key = self.mesh.split_edge(u, v, t=t, allow_boundary=True)
-            intersections.append(key)
+            if len(x) == sum([1 for i, j in zip(x, a) if i == j]):
+                intersections.append(u)
+            elif len(x) == sum([1 for i, j in zip(x, b) if i == j]):
+                intersections.append(v)
+            else:
+                L_ax = length_vector(subtract_vectors(x, a))
+                L_ab = length_vector(subtract_vectors(b, a))
+                t = L_ax / L_ab
+                key = self.mesh.split_edge(u, v, t=t, allow_boundary=True)
+                intersections.append(key)
         self._intersections = intersections
 
     def split(self):