Commit bc1fd8 introduced a thinko: We must not change
item_arg_cache->from_py_cleanup, as it's a global cache. Revert the original
change, and instead put the hack into _pygi_marshal_cleanup_from_py_array(),
which now short-circuits _pygi_marshal_cleanup_from_py_interface_struct_gvalue() to avoid
trying to release a slice which has never been allocated in
_pygi_marshal_from_py_array().

https://bugzilla.gnome.org/show_bug.cgi?id=672224