address: Set a dummy zipcode if none was returned from paypal

This is an attempt to fix a case where paypal does not provide any
zipcode back to us and then validation is failing. It is difficult
to test misconduct of paypal.

app/controllers/spree/checkout_controller_decorator.rb

@@ -100,6 +100,11 @@ module Spree
             order_ship_address.state_name = "N/A"
           end
 
+          # Paypal returned an address without zipcode
+          if order_ship_address.zipcode.nil?
+            order_ship_address.zipcode = "N/A"
+          end
+
           order_ship_address.save!
 
           @order.sysmocom_paypal_ship_address = order_ship_address