Only use glXCreateContext if glXCreateContextAttribsARB did not succeed.

Only use glXCreateContext if glXCreateContextAttribsARB did not succeed.

If glXCreateContextAttribsARB does not succeed or is not available,
we should fallback to using glXCreateContext. But we should not just
create a context with glXCreateContext by default that is being thrown
away if glXCreateContextAttribsARB succeeds.
Otherwise glXMakeCurrent with context 0 might cause an unexpected
context change when dealing with multiple contexts.

Change-Id: I7627abbe2500b4006180653a1b3b074fe7aca1d3
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>