CanvasContext.hasEinkScreen(): avoid crash on Android (#9417)
CanvasContext.hasEinkScreen(): avoid crash on Android (#9417)

It is used by CoverBrowser, in a subprocess, when extracting
metadata from PicDocuments, and crash on Android as calling
android methods is only allowed from the main thread.
poire-z/koreader,koreader/koreader,Frenzie/koreader,NiLuJe/koreader,koreader/koreader,poire-z/koreader,NiLuJe/koreader,Frenzie/koreader