Fix pager layout when $status_on_top with no mini-index. (closes #3836)

Fix pager layout when $status_on_top with no mini-index.  (closes #3836)

The pager_window->row_offset should only be adjusted when we have a
mini-index.

Pull common window initialization above, and adjust only when the
mini-index is enabled.  The pager_window rows and row_offset code
could be further consolidated (since the status line is always a
height of one), but I think the code reads a bit more clearly when the
adjustments are explicitly stated.