Fix logic issue in validate_fetch

Author: BoySanic

server/src/routes/validate_fetch.rs

@@ -42,8 +42,12 @@ pub async fn validate_fetch(
             tasks t
             JOIN assignments a ON
                 a.task_id = t.id
+            JOIN results r ON
+                r.assignment_id = a.id
         WHERE
             a.state = 'submitted'
+        AND
+            r.state = 'init'
         GROUP BY
             t.id
         HAVING