Commerce: `Order::EVENT_AFTER_ORDER_PAID` not firing for off site gateways

[Tam]

Description

Order::EVENT_AFTER_ORDER_PAID is not being fired for offsite gateways, specifically using the commerce-sagepay gateway.

Can confirm it is fired in 2.0.0-beta.13.1 but not 2.0.0-beta.14

Steps to reproduce

1. Complete a transaction via the SagePay gateway.

Additional info

• Craft version: Craft Pro 3.0.34
• PHP version: 7.1.19
• Database driver & version: PostgreSQL 9.5.14
• Plugins & versions: Craft Commerce 2.0.0-beta.14

[Tam]

I believe this is also the case when using a discount that reduces the order total to 0.

[benface]

This is happening for me when a Gift Voucher code brings the total of the order to $0. It's affecting any plugin that is listening to EVENT_AFTER_ORDER_PAID to do stuff when the order is paid, such as Digital Products (create licenses), Gift Voucher (update gift code amount), etc.

It seems to be a regression that was introduced in this commit: https://github.com/craftcms/commerce/commit/80f0f1c93f5db6173fd99a864bb9f4077b2d88b7

[wilcoreinders]

this is also happening when complete a transaction with a multisafepay extension or with a dummy payment.

[andris-sevcenko]

I see why this is happening. I'll do some testing to see if by fixing this I don't break anything else.