修复课程获取出错的BUG

app/controllers/attachments_controller.rb

@@ -87,8 +87,9 @@ class AttachmentsController < ApplicationController
       candown= User.current.member_of_course?(course) || (course.is_public==1 && @attachment.is_public == 1)
     elsif @attachment.container.class.to_s=="HomeworkAttach" && @attachment.container.bid.reward_type == 3
       candown = true
-    elsif  @attachment.container_type == "Bid" && @attachment.container && @attachment.container.courses
+    elsif  @attachment.container_type == "Bid" && @attachment.container && @attachment.container.courses.first
-      candown = User.current.member_of_course?(@attachment.container.courses.first) || (course.is_public == 1 && @attachment.is_public == 1)
+      course = @attachment.container.courses.first
+      candown = User.current.member_of_course?(course) || (course.is_public == 1 && @attachment.is_public == 1)
     else
 
       candown = @attachment.is_public == 1