epub: Fix thumbnailing of books with ePub 3.2 "cover-image"
Look for the "cover-image" manifest item property as defined in the EPUB 3.2 spec: https://www.w3.org/publishing/epub3/epub-packages.html#bib-epub32
Closes: #2 (closed)
Look for the "cover-image" manifest item property as defined in the EPUB 3.2 spec: https://www.w3.org/publishing/epub3/epub-packages.html#bib-epub32
Closes: #2 (closed)