don't use uninitialized face normals to compute vertex normals

tests/test_trimesh_normal_calculations.py

@@ -73,26 +73,14 @@ class Normals(unittest.TestCase):
         self.mesh.update_halfedge_normals()
 
     def test_calc_vertex_normal_fast(self):
-        self.mesh.request_vertex_normals()
-        self.mesh.request_halfedge_normals()
-        self.mesh.request_face_normals()
-
         n = self.mesh.calc_vertex_normal_fast(self.vhandle[2])
-        self.assertTrue(np.allclose(n, np.array([1, 2, 0])))
+        self.assertTrue(np.allclose(n, np.array([0.70710678, 0., -0.29289322])))
 
     def test_calc_vertex_normal_correct(self):
-        self.mesh.request_vertex_normals()
-        self.mesh.request_halfedge_normals()
-        self.mesh.request_face_normals()
-        
         n = self.mesh.calc_vertex_normal_correct(self.vhandle[2])
         self.assertTrue(np.allclose(n, np.array([1, 0, 0])))
 
     def test_calc_vertex_normal_loop(self):
-        self.mesh.request_vertex_normals()
-        self.mesh.request_halfedge_normals()
-        self.mesh.request_face_normals()
-        
         n = self.mesh.calc_vertex_normal_loop(self.vhandle[2])
         self.assertTrue(np.allclose(n, np.array([0.8660254, 0, 0])))