修复判断验证码是否存在的时候，用户不存在导致的报错

account/views.py

@@ -26,17 +26,15 @@ class UserLoginAPIView(APIView):
         serializer = UserLoginSerializer(data=request.data)
         if serializer.is_valid():
             data = serializer.data
-            user = User.objects.get(username=data["username"])
-            # 只有管理员才适用验证码登录
+            user = auth.authenticate(username=data["username"], password=data["password"])
+            # 用户名或密码错误的话 返回None
+            if user:
                 if user.admin_type > 0:
-                if not "captcha" in data:
+                    if "captcha" not in data:
                         return error_response(u"请填写验证码！")
                     captcha = Captcha(request)
                     if not captcha.check(data["captcha"]):
                         return error_response(u"验证码错误")
-            user = auth.authenticate(username=data["username"], password=data["password"])
-            # 用户名或密码错误的话 返回None
-            if user:
                 auth.login(request, user)
                 return success_response(u"登录成功")
             else: