xreader-thumbnailer dumps on a reasonable number of EPUB ebooks

[Jeremy7701]

 * Xreader version (xreader --version) Version of xreader=2.8.3     Version of xreader-thumbnailer=Unknown
 * Distribution - LMDE4

Issue
xreader-thumbnailer coredumps on EPUB files
For example https://termbin.com/dpzn

Steps to reproduce

Display a directory which causes nemo to request generation of a thumbnail?
It may not always dump, but it never produces a non-generic thumbnail.

Expected behaviour

Produce a Thumbnail!

Other information

All epub thumbnails produce a generic thumbnail - even books with a proper cover do not display one.

[Piiit]

@Jeremy7701 Hi, there is a PR I started long time ago... It needs further testing and it seems that there is a problem when be called from nemo, but it could be a draft for a final working epub thumbnailer... I would be happy if someone could take it over and finalize it...

#340

[clefebvre]

EPUB support was removed from Xreader and reimplemented in Xepub: https://github.com/xapp-project/xepub.