Don't truncate title in header line

[vlichevsky]

Looks like chapter title is truncated to the value of fb2-reader-page-width. It makes more sense to truncate it to the window width.

[jumper047]

Actually, I did it intentionally - like how it looks when truncated to page width:). But I agree - it is also a waste of useful space in the header line. I suppose there is should be an option.