FIX: Don't set smtp authentication type when there's no user or password

... otherwise net-smtp, starting with 0.5.0, complains.

config/environments/production.rb

@@ -31,12 +31,15 @@ Discourse::Application.configure do
       domain: GlobalSetting.smtp_domain,
       user_name: GlobalSetting.smtp_user_name,
       password: GlobalSetting.smtp_password,
-      authentication: GlobalSetting.smtp_authentication,
       enable_starttls_auto: GlobalSetting.smtp_enable_start_tls,
       open_timeout: GlobalSetting.smtp_open_timeout,
       read_timeout: GlobalSetting.smtp_read_timeout,
     }
 
+    if settings[:password] || settings[:user_name]
+      settings[:authentication] = GlobalSetting.smtp_authentication
+    end
+
     settings[
       :openssl_verify_mode
     ] = GlobalSetting.smtp_openssl_verify_mode if GlobalSetting.smtp_openssl_verify_mode