fix internal path column

Kind of a slight oversight, but the callback assignment page shows the INTERNAL PATH column, but it instead displays "NO TITLE", when it should probably display the internal path instead.

But it would be nice if PAGE TITLE was the first column, and INTERNAL PATH was the second column anyway.

I'm new to D8, so I'm not capable of editing the EmptyPageController.php file to display another column, but I think that's where it is.