filemanagershortcuts: fix adding the first shortcut (#9107)
filemanagershortcuts: fix adding the first shortcut (#9107)

Closes #9105.
poire-z/koreader,NiLuJe/koreader,Frenzie/koreader,poire-z/koreader,NiLuJe/koreader,koreader/koreader,Frenzie/koreader,koreader/koreader