fix: three bugs in highlight mode
fix: three bugs in highlight mode

* handle left end of first line in cursor move
* properly highlight first word if cursor starts
  from left end of first line
* handle right end of last line in cursor move

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