Avoid crash if trying to open a non-existent file
Avoid crash if trying to open a non-existent file

which currently might occur by clicking in the history entry of a file which was removed

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