reader without mut

app/src/main.rs

@@ -232,7 +232,7 @@ fn main() {
 }
 
 fn read_from_db2(id: u32) -> Option<Question> {
-    let mut reader: db::Reader<Question> =
+    let reader: db::Reader<Question> =
         db::Reader::new(NEW_DB_FILENAME, 2048).expect("new db reader");
 
     let mut questions = reader.iter();