Update readerscreenshot.lua
Update readerscreenshot.lua

Somehow the required lines have gone missing, resulting in a crash every time I tried to get a screenshot.

Anybody know why the got deleted?
poire-z/koreader,Frenzie/koreader,Markismus/koreader,robert00s/koreader,lgeek/koreader,mihailim/koreader,poire-z/koreader,chihyang/koreader,Hzj-jie/koreader,mwoz123/koreader,chrox/koreader,ashang/koreader,noname007/koreader,koreader/koreader,NickSavage/koreader,ashhher3/koreader,pazos/koreader,Frenzie/koreader,houqp/koreader,NiLuJe/koreader,koreader/koreader,NiLuJe/koreader,apletnev/koreader,frankyifei/koreader