Always give sane output for Title::getUserCaseDBkey()

Sometimes (e.g. via Title::makeTitle), the usercase db key is
not set. If that happens we should fallback to the normal db key.

This fixes file redirects on repos where initialCapital is set
to false.

Change-Id: I38bc4ebeb41b06f5c718cf5f64da158e6c1a9f49
Merge "Always give sane output for Title::getUserCaseDBkey()"