OBJLoader: Fix material copy for lines and point clouds

[Mugen87]

Fixes: #15175

It's not correct to use LineBasicMaterial.copy() or PointsMaterial.copy() if the given material parameter is a phong material.

Now, OBJLoader uses Material.copy() in order to copy common properties. The PR also fixes the wrong usage of materialLine in context of PointsMaterial. I assume this was a copy/paste error.

I've tested with this test.obj file:

# Blender v2.79 (sub 0) OBJ File: ''
# www.blender.org
mtllib test.mtl
o Cube
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 1.000000 -0.999999
v 0.999999 1.000000 1.000001
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000

p 1 2 3 4 5 6 7 8

Just add an empty MTL file for testing.

[mrdoob]

Thanks!