Update DivinerAtomController for a long-ago change to the docblock parser API
Summary: Ref T13505. See that task for discussion.
Test Plan: Ran `diviner generate` locally, found a page fataling on this `strlen()`, applied patch, got a sketchy but not-broken page.
Maniphest Tasks: T13505
Differential Revision: https://secure.phabricator.com/D21061