Bump libk2pdfopt (#563)
Bump libk2pdfopt (#563)

Includes:
* implement pixmap_to_bmp https://github.com/koreader/libk2pdfopt/pull/28
* Leptonica 1.73+ support https://github.com/koreader/libk2pdfopt/pull/29
apletnev/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,Frenzie/koreader-base,houqp/koreader-base,apletnev/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,Frenzie/koreader-base,Frenzie/koreader-base,houqp/koreader-base,apletnev/koreader-base,Frenzie/koreader-base,apletnev/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,koreader/koreader-base