FIX: Correctly use invite to topic email templates (#12411)

It was used both when inviting from a topic page and when creating
invites with "Send to topic on first login", while it should be used
only in the former case.

app/mailers/invite_mailer.rb

@@ -5,7 +5,7 @@ class InviteMailer < ActionMailer::Base
 
   layout 'email_template'
 
-  def send_invite(invite)
+  def send_invite(invite, invite_to_topic: false)
     # Find the first topic they were invited to
     first_topic = invite.topics.order(:created_at).first
 
@@ -19,7 +19,7 @@ class InviteMailer < ActionMailer::Base
       ActionView::Base.full_sanitizer.sanitize(invite.custom_message.gsub(/\n+/, " ").strip) : nil
 
     # If they were invited to a topic
-    if first_topic.present?
+    if invite_to_topic && first_topic.present?
       # get topic excerpt
       topic_excerpt = ""
       if first_topic.excerpt