Set max mipmap level to zero when not using mipmaps

When using the opengl debug extension I get flooded by these messages:

```Type: Other, Source: API, ID: 131204, Severity: Low, Message: Texture state usage warning: Waste of memory: Texture 0 has mipmaps, while it's min filter is inconsistent with mipmaps.```

Setting the max mipmap level to zero (default is 1000) stops the warning, all other parameters seem to be correct.
I don't think there's actually any memory wasted, but I don't think nvidia is considering this a driver issue since it's been this way for as long as I remember.