(Bug 43752) Don't attempt to render null rev ids.

References:

Title::inNamespace:
http://svn.wikimedia.org/doc/classTitle.html#a17bd50bacfacf339375970d15860861a

Title::isKnown:
http://svn.wikimedia.org/doc/classTitle.html#a1f5bed50434c2b5da7ef89df18769226

Change-Id: I3da5f5f6343876b28c67bdd988f33ec5c5f8b95b