When a callback list is initialized using CreateCallbackList via AddCallback,
the list gets added to the listsToCleanup array, and as a result the list gets
deleted at the end of the server generation.
But, vendor libraries add themselves to that callback list only once, not once
per generation, so if you delete the list, then no vendor will register itself
on the next generation, and GLX breaks.
Instead, use a static CallbackListRec for the extensionInitCallback list. That
way, it doesn't get added to listsToCleanup, and doesn't get deleted during a
reset.
Reviewed-by: Adam Jackson <ajax@redhat.com>
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