修复用户提交题目的时候，problems_status 中没有对应的 key 导致的错误

submission/views.py

@@ -54,6 +54,8 @@ class SubmissionAPIView(APIView):
                 return error_response(u"提交判题任务失败")
             # 修改用户解题状态
             problems_status = request.user.problems_status
+            if "problems" not in problems_status:
+                problems_status["problems"] = {}
             problems_status["problems"][str(data["problem_id"])] = 2
             request.user.problems_status = problems_status
             request.user.save()