Including C headers inside of `extern "C"` breaks use from C++. Hoist
the includes of standard C headers above the block so we don't try
to mangle the stdlib.
I initially tried to scope this with a targeted change but it's too
hard to do correctly that way. This way, we avoid whack-a-mole.
Firefox is working around this in their e21461b7b8b39cc31ba53c47d4f6f310c673ff2f
commit.
Bug: https://bugzilla.mozilla.org/1953080
What may be NULL in these methods is the pointer to the object
containing the spa_interface, not the interface pointer itself.
Fixes spa-acp-tool crashing with NULL deref in spa_i18n.
The Doxygen "Modules" page is not very illuminative, as different parts
of the API are mixed together and not all parts are included.
Try to address this:
Put all parts of the public API to some Doxygen group, usually one group
per header file. Use short, systematic names.
Make these groups sub-groups of a few top-level groups, roughly
corresponding to the different logical parts of the API (core, impl,
stream, filter, spa, utilities).
Subdirectories buffer, control, debug, monitor, pod, support and utils, others
are still missing. Headers are grouped either per subdirectory (e.g. buffer/
gets added to group spa_buffer) or per-file (e.g. spa_json is a separate
group), whatever seemed like the most sensible approach.
