Avoid PageUpdate from receiving out-of-range page
Avoid PageUpdate from receiving out-of-range page

Otherwise, current_page can acquire negative values, or values greater
than the page count, when the user tries to go back the first page
or past the last page.

ashhher3/koreader,frankyifei/koreader,Frenzie/koreader,Hzj-jie/koreader,koreader/koreader,mwoz123/koreader,koreader/koreader,noname007/koreader,NiLuJe/koreader,chrox/koreader,poire-z/koreader,apletnev/koreader,Frenzie/koreader,pazos/koreader,NiLuJe/koreader,poire-z/koreader,robert00s/koreader,mihailim/koreader,NickSavage/koreader,lgeek/koreader,ashang/koreader,Markismus/koreader,chihyang/koreader,houqp/koreader