Initialize watcher_user_ids for new records to prevent useless queries on each #watched_by?.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@8554 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/issue.rb

@@ -119,6 +119,7 @@ class Issue < ActiveRecord::Base
       # set default values for new records only
       self.status ||= IssueStatus.default
       self.priority ||= IssuePriority.default
+      self.watcher_user_ids = []
     end
   end