This updates many places where 0 is used as NULL pointer.
There are a few warnings left when I build the default
configuration but they either relate to code
outside of mesa or where "None" is used instead.
Found with static analysis (smatch)
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12174>