Blender Git Loki

Fix crash for Windows+Intel video card configuration

Intel video cards don't work fine with multiple contexts and
have to share the same context for all windows. This could work
incorrect with multiple video cards configuration, so suppose
there'll be no such situation (Intel cards are mostly in portable
devices like notebooks and laptops, where there's actually no
dual video cards). Anyway, it should work much better now.

Non-Intel cards behavior was kept unchanged.

Thanks to Ton for debug session :)