Fix AMD render problem with missed meshes.

Fixes an issue when rendering certain meshes on AMD cards

Example mesh rendering on a 6870:
![15kv-amd-bad](https://cloud.githubusercontent.com/assets/8334203/5368113/fe3f91a0-7fcf-11e4-85b5-dc08579e8e22.jpg)

Should look like this:
![15kv-amd-good](https://cloud.githubusercontent.com/assets/8334203/5368123/20f540aa-7fd0-11e4-8dbf-810e563cf5b3.jpg)

dae (thanks to Nadeox for the test case):
https://www.dropbox.com/s/dvew91p97nxt2pc/15kV.dae?dl=0

Note: This is a bugfix by Luis, but I am using this as a safe jumping-off point for contributing to t3d. Hi everyone :)