fix filechooser crash on entering folder contains nil symlink

frontend/ui/widget/filechooser.lua

@@ -57,13 +57,15 @@ function FileChooser:genItemTableFromPath(path)
             if self.show_hidden or not string.match(f, "^%.[^.]") then
                 local filename = self.path.."/"..f
                 local attributes = lfs.attributes(filename)
-                if attributes.mode == "directory" and f ~= "." and f~=".." then
-                    if self.dir_filter(filename) then
-                        table.insert(dirs, {name = f, attr = attributes})
-                    end
-                elseif attributes.mode == "file" then
-                    if self.file_filter(filename) then
-                        table.insert(files, {name = f, attr = attributes})
+                if attributes ~= nil then
+                    if attributes.mode == "directory" and f ~= "." and f~=".." then
+                        if self.dir_filter(filename) then
+                            table.insert(dirs, {name = f, attr = attributes})
+                        end
+                    elseif attributes.mode == "file" then
+                        if self.file_filter(filename) then
+                            table.insert(files, {name = f, attr = attributes})
+                        end
                     end
                 end
             end