Fix crash when trying to go to / on FM
Fix crash when trying to go to / on FM

Deals with more cases in FileChooser:compressPath, including `/mnt/..`.

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