dmails: only spam check recipient's copy of the dmail.

Each dmail creates two copies, one for the sender and one for the
receiver. Only spam check the receiver's copy.

Prevents senders from being able to tell when their messages are being
spam filtered.

app/models/dmail.rb

@@ -31,9 +31,9 @@ class Dmail < ApplicationRecord
       creator_ip_addr.to_s
     end
 
-    def spam?(sender = CurrentUser.user)
+    def spam?
       return false if Danbooru.config.rakismet_key.blank?
-      return false if sender.is_gold?
+      return false if from.is_gold?
       super()
     end
   end
@@ -58,7 +58,6 @@ class Dmail < ApplicationRecord
     def initialize_attributes
       self.from_id ||= CurrentUser.id
       self.creator_ip_addr ||= CurrentUser.ip_addr
-      self.is_spam = spam?(CurrentUser.user)
     end
   end
 
@@ -73,6 +72,7 @@ class Dmail < ApplicationRecord
           # recipient's copy
           copy = Dmail.new(params)
           copy.owner_id = copy.to_id
+          copy.is_spam = copy.spam?
           copy.save unless copy.to_id == copy.from_id
 
           # sender's copy

test/unit/dmail_test.rb

@@ -23,8 +23,8 @@ class DmailTest < ActiveSupport::TestCase
 
       should "not validate" do
         assert_difference("Dmail.count", 2)do
-          dmail = Dmail.create_split(:to_id => @recipient.id, :title => "My video", :body => "hey Noneeditsonlyme.  My webcam see here http://bit.ly/2vTv9Ki")
-          assert(dmail.is_spam?)
+          Dmail.create_split(:to_id => @recipient.id, :title => "My video", :body => "hey Noneeditsonlyme.  My webcam see here http://bit.ly/2vTv9Ki")
+          assert(@recipient.dmails.last.is_spam?)
         end
       end
     end