correcly grap name, omit needless query

app/mailers/user_notifications.rb

@@ -188,7 +188,8 @@ class UserNotifications < ActionMailer::Base
 
     user_name = @notification.data_hash[:original_username]
     if @post && SiteSetting.enable_names && SiteSetting.display_name_on_posts
-      user_name = User.find_by(id: @post.user_id).name if !User.find_by(id: @post.user_id).name.empty?
+      name = User.where(id: @post.user_id).pluck(:name).first
+      user_name = name unless name.blank?
     end
 
     notification_type = opts[:notification_type] || Notification.types[@notification.notification_type].to_s