Fix for r81675: Skin::getTitle() will return null when $wgTitle is null and $wgOut...

Fix for r81675: Skin::getTitle() will return null when $wgTitle is null and $wgOut->setTitle() not called, resulting in the following when passing a non-null parameter to User::getSkin():
Catchable fatal error: Argument 1 passed to Title::equals() must be an instance of Title, null given, called in includes/User.php on line 2255 and defined in includes/Title.php on line 3689