Fix regression #5467: fixes emoji copy (#5739)

app/controllers/admin/custom_emojis_controller.rb

@@ -45,9 +45,10 @@ module Admin
     def copy
       authorize @custom_emoji, :copy?
 
-      emoji = CustomEmoji.find_or_create_by(domain: nil, shortcode: @custom_emoji.shortcode)
+      emoji = CustomEmoji.find_or_initialize_by(domain: nil, shortcode: @custom_emoji.shortcode)
+      emoji.image = @custom_emoji.image
 
-      if emoji.update(image: @custom_emoji.image)
+      if emoji.save
         flash[:notice] = I18n.t('admin.custom_emojis.copied_msg')
       else
         flash[:alert] = I18n.t('admin.custom_emojis.copy_failed_msg')