Fiction Book Reader: fixed loading books from an SD card

Dear users of the Windows Phone 8 reader: if your phone has an SD card, I have very good news for you. Today I bought myself a test device that supports memory cards (Lumia 820), and after literally 5 minutes of debugging I found the bug in the code that made it impossible to open books from a memory card in any folder other than the root.

An update will be released soon.