We had some code that tried to reuse the context over realize, but
that doesn't work as we need to share with the possibly new
paint context of the re-realized window.
Its not really reasonable to handle failures to make_current, it
basically only happens if you pass invalid arguments to it, and
thats not something we trap on similar things on the X drawing side.
If GL is not supported that should be handled by the context creation
failing, and anything going wrong after that is essentially a critical
(or an async X error).
