fix #1569 use fit to page zoom cover image even in reflow mode
fix #1569 use fit to page zoom cover image even in reflow mode

NiLuJe/koreader,chihyang/koreader,Markismus/koreader,houqp/koreader,Frenzie/koreader,lgeek/koreader,koreader/koreader,poire-z/koreader,koreader/koreader,apletnev/koreader,robert00s/koreader,mihailim/koreader,poire-z/koreader,Frenzie/koreader,NickSavage/koreader,NiLuJe/koreader,mwoz123/koreader,frankyifei/koreader,Hzj-jie/koreader,pazos/koreader