Blender Git Loki

Fix T42349: Windows Render command line Cycles Crash

The issue was caused by GLEW MX enabled in SCons by default so
basically previous commit already fixed the crash. But we need
to be safe here.

For now the fix is simple and not that clean, just check if
there's an OpenGL context available and if not we don't do any
GLSL magic.

This is to be cleaned up after some discussion with the viewport
project guys.