FIX: Show inviter name in email's from field (#13141)

'From' field of the email contained the name of the user who posted the
shared post. Instead, it should contain the name of the inviter.

app/mailers/user_notifications.rb

@@ -422,7 +422,7 @@ class UserNotifications < ActionMailer::Base
     user_name = notification_data[:original_username]
 
     if post && SiteSetting.enable_names && SiteSetting.display_name_on_email_from
-      name = User.where(id: post.user_id).pluck_first(:name)
+      name = User.where(id: notification_data[:original_user_id] || post.user_id).pluck_first(:name)
       user_name = name unless name.blank?
     end