eina: Applied NULL check

eina: Applied NULL check

Summary:
In _eina_list_setup_accounting function
{
...
...
if (!list->accounting)
     goto on_error;
...
...
on_error:
   _eina_list_mempool_list_free(list);
}

_eina_list_mempool_list_free function deference the "list->accounting"
variable which is already NULL.

Reviewers: JackDanielZ, jpeg

Reviewed By: jpeg

Subscribers: cedric, jpeg

Differential Revision: https://phab.enlightenment.org/D3376