Adding a payment to an order without any strategies crashes

Problem/Motivation

Follow-up from #3584202: Call to a member function canCapturePayment() on null that I encountered when testing.

TypeError: Drupal\commerce_xero\CommerceXeroDataManager::createData(): argument #2 ($strategy) must be of  type Drupal\commerce_Entity\CommerceXeroStrategyInterface, null given, called in /var/www/html/web/modules/contrib/commerce_xero/src/EventSubscriber/OrderSubscriber.php on line 113 in Drupal\commerce_xero\CommerceXeroDataTypeManager->createData() (line 58 of /var/www/html/web/modules/contrib/commerce_xero/src/CommerceXeroDataTypeManager.php).

Steps to reproduce

1. Prepare a commerce environment with a store, product, product variation, manual payment gateway
2. Install Commerce Xero
3. Create an order for the product
4. Add a payment for the order
5. Receive the payment on the order

Proposed resolution

Prevent OrderSubscriber from doing anything if there are no strategies found.

Remaining tasks