Pan-Zoom: current magnification value is reset when switching to a reflow from a fixed-layout page, and back to FXL

[danielweck]

Test EPUB: Recollections of Wartime (Infogrid Pacific) http://azardi.infogridpacific.com/resources.html

Excepted result: current zoom value should be preserved even after having switched to reflow documents (spine items can be mixed FXL / reflow).