Prevents validation error when adding a user to a group (#6457).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4437 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/group.rb

@@ -31,6 +31,7 @@ class Group < Principal
   
   def user_added(user)
     members.each do |member|
+      next if member.project.nil?
       user_member = Member.find_by_project_id_and_user_id(member.project_id, user.id) || Member.new(:project_id => member.project_id, :user_id => user.id)
       member.member_roles.each do |member_role|
         user_member.member_roles << MemberRole.new(:role => member_role.role, :inherited_from => member_role.id)