When loading a one page document, and when zooming it (ie to see name streets on a map), if Okular is in facing pages view mode, the scroll system doesn't allow us to see the left part of the page, but allow us to see far away right of this page.

I think the limit of the viewport are wrongly computed.

Two solutions : 
 - let okular act like in "single page mode" whatever the setting is when the document contains only one page (I think it's the best choice)
 - change the setting to "single page mode" when opening this kind of document (perhaps easier to implement ?)

Reproducible: Always

Steps to Reproduce:
1. Open the map given in url
2. Choose View / View mode / Facing Pages
3. Try to scroll to the left of the document
Actual Results:  
I'm unable to see the Eiffel tower on the map, because it is impossible to scroll to the left.

Expected Results:  
I should be able to scroll the entire document, whatever the settings are.

The bug can be reproduced with any one page pdf. I didn't try with other kind of document, but I think the problem is not bound with the document type.