bugfix

Fixes: https://github.com/refinery/refinerycms-blog/issues/367
Maybe fixes: https://github.com/refinery/refinerycms-blog/issues/361 https://github.com/refinery/refinerycms-blog/pull/363 https://github.com/refinery/refinerycms-blog/issues/365 https://github.com/refinery/refinerycms-blog/issues/342

HOW TO FIX older posts:
1) pull this fix
2) Start rails console (rails c)
3) In rails console run command:  ::Refinery::Blog::Post.find_each(&:save)

And it should be ok. It is for me...
you can use `@post.nil?`