Nav bar hides horizontal scroll bar in 2up mode

Situation: viewing a document in 2-up (facing page) mode, zoomed in such that all outside edges of the pages are outside the document viewable area.

Behaviour: if the Nav bar at the bottom is visible, it covers the horizontal scroll bar at the bottom. This scroll bar is the only way to move the viewable area around to view the far left or right areas of the current pages in 2-up mode.

Potential solution: show a second scroll bar above the nav bar when necessary, and remove it when the nav bar is closed.