优化下载权限判断

app/controllers/attachments_controller.rb

@@ -67,6 +67,8 @@ 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
+    else
+      candown = @attachment.is_public == 1
     end
     if candown || User.current.admin?
       @attachment.increment_download