Avoid repetitive load relationship.

models/judge_state.js

@@ -101,9 +101,13 @@ class JudgeState extends Model {
   }
 
   async loadRelationships() {
+    if (!this.user) {
       this.user = await User.fromID(this.user_id);
+    }
+    if (!this.problem) {
       if (this.problem_id) this.problem = await Problem.fromID(this.problem_id);
     }
+  }
 
   async isAllowedVisitBy(user) {
     await this.loadRelationships();