[fix, plugins] Wallabag: close document on go to folder (#5063)

See https://github.com/koreader/koreader/issues/5060#issuecomment-499416617

plugins/wallabag.koplugin/main.lua

@@ -109,6 +109,9 @@ function Wallabag:addToMainMenu(menu_items)
             {
                 text = _("Go to download folder"),
                 callback = function()
+                    if self.ui.document then
+                        self.ui:onClose()
+                    end
                     if FileManager.instance then
                         FileManager.instance:reinit( self.directory )
                     else