MalformedTitleException should call parent::__construct

MalformedTitleException should call parent::__construct

There's no reason for $ex->getMessage() to return nothing. Do like
ErrorPageError does and get the default English message for the parent.

Also move the appending of $titleText to $errorMessageParameters into
MalformedTitleException itself and document it, so every catcher of the
exception doesn't need to know about this, and fix the check so it
doesn't screw up for title "0".

Change-Id: I43d988602b847b67a3cf0aa84e271a0b5bd9adae