[RFC] vim-patch:7.4.369

7.4.369:

> Problem:    Using freed memory when exiting while compiled with EXITFREE.
> Solution:   Set curwin to NULL and check for that. (Dominique Pelle)

https://code.google.com/p/vim/source/detail?r=v7-4-369

Original code in neovim uses `if (buf->b_signlist == NULL)` instead of `if (buf->b_signlist != NULL)`.
It seems bug...