Move 'main page as default title' further down to unbreak diff urls

The feature that oldid and diff parameters override the title was
not working if wiki's main page is a special page, because that
behaviour was excluded for special pages. Hence moved the main
page as default title code further down, so that we will hit the
no title provided condition for the oldid and diff parameter only
links.

Bug: 54452
Change-Id: I62cc6e2568a4db988fcf113955ba02710e42a1d2