xreader: special characters are wrong in index/outline #608

 * xreader 3.2.2
 * Linux Mint 20.3 Una amd64

Issue

I have ebook written in Czech language and I see that several Czech characters are not displayed correctly in the index/outline. Content of the book is rendered correctly, I see issue only in the Index. I see that when I open the same book in the Brave browser (it has internal PDF reader), I cannot see this bug, so I assume that ebook is generated correctly and the bug is in the xreader

Steps to reproduce

Download eBook, open it in xreader and check Index on the left.

Expected behaviour

Index:

• 1 přední
• 21 lekcí_print_vers1
• 2 zadní
  

Other information
I have found other ebook example and in this book I cannot see this issue, Index has correct characters. So it looks like only some ebooks trigger this issue and others are ok...