fix(cre): return nil for no text mathced in getTextFromPositions
fix(cre): return nil for no text mathced in getTextFromPositions

frankyifei/koreader-base,NiLuJe/koreader-base,Frenzie/koreader-base,Hzj-jie/koreader-base,apletnev/koreader-base,koreader/koreader-base,koreader/koreader-base,Frenzie/koreader-base,Hzj-jie/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,houqp/koreader-base,frankyifei/koreader-base,Frenzie/koreader-base,frankyifei/koreader-base,koreader/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,apletnev/koreader-base,NiLuJe/koreader-base,frankyifei/koreader-base,Frenzie/koreader-base,houqp/koreader-base,Hzj-jie/koreader-base,Hzj-jie/koreader-base,apletnev/koreader-base,houqp/koreader-base,houqp/koreader-base