fixed bugs in implementation of utf8Chars()
fixed bugs in implementation of utf8Chars()

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