ABN-298/fix: total collector guard — check items, not address type

The address type check could return early on valid assignments where
getAddressType() was empty. Use the standard Magento pattern of
checking for items in the shipping assignment instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dgjlindsay

Model/Total/Surcharge.php

@@ -64,8 +64,8 @@ public function collect(
     ): self {
         parent::collect($quote, $shippingAssignment, $total);
 
-        // Only run on the shipping address (avoid double-counting on billing)
-        if (!$shippingAssignment->getShipping()->getAddress()->getAddressType()) {
+        // Only run when there are items (avoids double-counting on empty assignments)
+        if (!count($shippingAssignment->getItems())) {
             return $this;
         }