save attachment before copy to new namespace

fixes CNVS-35913

test plan
 - copy attachment to course in different root_account
 - it should work

Change-Id: I1b4e99331b2299960522ac628ff3a2cbce27873c
Reviewed-on: https://gerrit.instructure.com/107024
Tested-by: Jenkins
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>

app/models/attachment.rb

@@ -279,6 +279,7 @@ class Attachment < ActiveRecord::Base
       context.log_merge_result("File \"#{dup.folder && dup.folder.full_name}/#{dup.display_name}\" created")
     end
     if context.respond_to?(:root_account_id) && self.namespace != context.root_account.file_namespace
+      dup.save_without_broadcasting!
       dup.make_rootless
       dup.change_namespace(context.root_account.file_namespace)
     end

spec/models/attachment_spec.rb

@@ -580,6 +580,7 @@ describe Attachment do
       @context = courseb = course_factory(account: Account.create)
 
       b = a.clone_for(courseb, nil, overwrite: true)
+      expect(b.id).not_to be_nil
       b.save
       expect(b.root_attachment_id).to eq nil
       expect(b.namespace).to eq courseb.root_account.file_namespace