FIX: Unexpected return during system_message_sent event

Followup to 0bb51dc, should fix an issue with multiple system message events being sent

plugins/discourse-narrative-bot/plugin.rb

@@ -287,8 +287,7 @@ after_initialize do
   )
 
   self.on(:system_message_sent) do |args|
-    return if args[:message_type] != 'tl2_promotion_message'
-    return if !SiteSetting.discourse_narrative_bot_enabled
+    if args[:message_type] == 'tl2_promotion_message' && SiteSetting.discourse_narrative_bot_enabled
 
       raw = I18n.t("discourse_narrative_bot.tl2_promotion_message.text_body_template",
                   discobot_username: ::DiscourseNarrativeBot::Base.new.discobot_username,
@@ -302,6 +301,7 @@ after_initialize do
         skip_validations: true
       )
     end
+  end
 
   PostGuardian.class_eval do
     alias_method :existing_can_create_post?, :can_create_post?