[GPU-Z Test Build] Fix for crash w/ NVIDIA cards and ATI Stream SDK

[Stefan]

[GPU-Z Test Build] Fix for crash w/ NVIDIA cards and ATI Stream SDK
- Fixes a crash in OpenCL detection on NVIDIA cards, when the ATI Stream SDK is installed.
For some reason AMD's driver still loads even though no ATI card is installed in the system.

- Also fixed, rounding error when calculating Texture Fillrate on NVIDIA cards

Yet fails with Cedar...