fix bug in highlight engine
fix bug in highlight engine

handle left end of line in highlight delete.

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