Material color is merged with texture, even if opaque

```
What steps will reproduce the problem?
In the viewer, open an object that contains a black mesh that has an opaque
texture

What is the expected output? What do you see instead?
The mesh is shown black and the texture is not visible.
You should only see the texture on the mesh.

What version of the product are you using? On what operating system?
Problem exists on the latest SVN revision

Please provide any additional information below.
You can find attached 2 3D objects, both with a texture but one has black
material and the other has white. They should render the same way.
```

Original issue reported on code.google.com by `laurent....@fabzat.com` on 18 Mar 2014 at 8:54

Attachments:
- [textured_cubes.zip](https://storage.googleapis.com/google-code-attachments/jsc3d/issue-70/comment-0/textured_cubes.zip)

Start by reproducing the problem in the viewer with the attached textured_cubes.zip objects, comparing the black-material and white-material cases. Trace the rendering path where material color and texture are combined. Done means both objects render the texture identically when the material is opaque.

Written by the indexing model from the issue text.