#260 position isn't saving before switching to another book

[student975]

I have reproduced the issue 5-6 times sequentially without exceptions (100% reproducible). Streps:

- open a book; let is be bookA, and last saved position is pos1
- navigate to some another positions; let it be pos2
- switch to another book
- close the reader
- kill background process
- start the reader
- switch to bookA

Result: the book is opened at pos1
Expected: the book is opened at pos2

[idleloop]

This bug must be extended:
Cool reader does not save any changes made to a book (position, bookmarks, corrections) before switching to another book.
Reproducible always.
In order to save changes, one must manually close cool reader.