fix context overriding: - do not crash if context overriding fails - try to query glXGetProcAddressARB via extension mechanism,   fixes issues if libGL.so doesn't export that symbol
fix context overriding:
- do not crash if context overriding fails
- try to query glXGetProcAddressARB via extension mechanism,
  fixes issues if libGL.so doesn't export that symbol

derhass/glx_hook