Fixed some ineffective assignments (#12543)

config/migrate.go

@@ -42,6 +42,9 @@ func migrateFile(name string, source Store, destination Store) error {
 
 	if fileExists {
 		file, err := source.GetFile(name)
+		if err != nil {
+			return errors.Wrapf(err, "failed to migrate %s", name)
+		}
 		err = destination.SetFile(name, file)
 		if err != nil {
 			return errors.Wrapf(err, "failed to migrate %s", name)