Fix weird case: mention of post without title?!? (happened)

I have no idea why this happens when I mention [this](https://dubiousdod.org/indie/2014/11/repost-of-mondoweiss-net-2014-11-thanksgiving-holiday) (seems to have a title), but with this fix [mentions](https://dubiousdod.org/indie/mentions) don't crash :wink: