app_async: fix print random question

app_async/src/main.rs

@@ -154,7 +154,7 @@ async fn read_from_db(id: u32) -> Option<Question> {
 
     let len = reader.len();
 
-    let index = if len == 0 {
+    let index = if id == 0 {
         let mut rng = thread_rng();
         let questions = Uniform::new(0, len);
         rng.sample(questions)