Investigate additional is_array checks in SV_WC_Helper::array_to_xml()

[bekarice]

With the latest XML Export version, when iterating over order xml, I'm getting warnings for an invalid foreach argument:

Stack trace

PHP Warning:  Invalid argument supplied for foreach() in /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/class-sv-wc-helper.php on line 340
PHP Stack trace:
PHP   1. {main}() /wp-admin/admin-ajax.php:0
PHP   2. do_action() /wp-admin/admin-ajax.php:101
PHP   3. WP_Hook->do_action() /wp-includes/plugin.php:453
PHP   4. WP_Hook->apply_filters() /wp-includes/class-wp-hook.php:323
PHP   5. SV_WP_Background_Job_Handler->maybe_handle() /wp-includes/class-wp-hook.php:298
PHP   6. SV_WP_Background_Job_Handler->handle() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/utilities/class-sv-wp-background-job-handler.php:131
PHP   7. SV_WP_Background_Job_Handler->process_job() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/utilities/class-sv-wp-background-job-handler.php:542
PHP   8. WC_Customer_Order_XML_Export_Suite_Background_Export->process_item() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/utilities/class-sv-wp-background-job-handler.php:607
PHP   9. WC_Customer_Order_XML_Export_Suite_Handler->export_item() /woocommerce-customer-order-xml-export-suite/includes/class-wc-customer-order-xml-export-suite-background-export.php:77
PHP  10. WC_Customer_Order_XML_Export_Suite_Generator->get_output() /woocommerce-customer-order-xml-export-suite/includes/class-wc-customer-order-xml-export-suite-handler.php:721
PHP  11. WC_Customer_Order_XML_Export_Suite_Generator->get_orders_xml() /woocommerce-customer-order-xml-export-suite/includes/class-wc-customer-order-xml-export-suite-generator.php:1304
PHP  12. WC_Customer_Order_XML_Export_Suite_Generator->get_xml() /woocommerce-customer-order-xml-export-suite/includes/class-wc-customer-order-xml-export-suite-generator.php:191
PHP  13. SV_WC_Helper::array_to_xml() /woocommerce-customer-order-xml-export-suite/includes/class-wc-customer-order-xml-export-suite-generator.php:1221
PHP  14. SV_WC_Helper::array_to_xml() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/class-sv-wc-helper.php:354
PHP  15. SV_WC_Helper::array_to_xml() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/class-sv-wc-helper.php:341
PHP  16. SV_WC_Helper::array_to_xml() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/class-sv-wc-helper.php:354
PHP  17. SV_WC_Helper::array_to_xml() /woocommerce-customer-order-xml-export-suite/lib/skyverge/woocommerce/class-sv-wc-helper.php:341

It looks like we're walking to the end of the array and trying to then walk a string instead potentially, as the array before conversion looks fine:

Logged order export

Array
(
  [Order] => Array
    (
      [0] => Array
        (
          [OrderId] => 1159
          [OrderNumber] => 1159
          [OrderDate] => 2017-07-25 14:57:23
          [OrderStatus] => processing
          [BillingFirstName] => Walter
          [BillingLastName] => White
          [BillingFullName] => Walter White
          [BillingCompany] => 
          [BillingAddress1] => 308 Negra Arroyo Lane
          [BillingAddress2] => 
          [BillingCity] => Albuquerque
          [BillingState] => NM
          [BillingPostCode] => 87104
          [BillingCountry] => US
          [BillingEmail] => heisenberg@mailinator.com
          [BillingPhone] => 5558675309
          [ShippingFirstName] => Walter
          [ShippingLastName] => White
          [ShippingFullName] => Walter White
          [ShippingCompany] => 
          [ShippingAddress1] => 308 Negra Arroyo Lane
          [ShippingAddress2] => 
          [ShippingCity] => Albuquerque
          [ShippingState] => NM
          [ShippingPostCode] => 87104
          [ShippingCountry] => US
          [ShippingMethodId] => local_pickup_plus
          [ShippingMethod] => Store Pickup
          [PaymentMethodId] => bogus_gateway
          [PaymentMethod] => Bogus (Test)
          [DiscountTotal] => 0
          [ShippingTotal] => 10.8
          [ShippingTaxTotal] => 0.00
          [OrderTotal] => 226.80
          [FeeTotal] => 0
          [TaxTotal] => 0.00
          [CompletedDate] => 
          [CustomerNote] => 
          [CustomerId] => 2
          [OrderLineItems] => Array
            (
              [0] => Array
                (
                  [SKU] => 
                  [Quantity] => 1
                  [Price] => 216.00
                  [Meta] => Length (ft): 12, Width (ft): 3, Total Area (sq. ft.): 36
                  [ItemName] => Tarp
                  [LineTotal] => 216.00
                )
        )

      [OrderNotes] => Array
        (
          [OrderNote] => Array
            (
              [0] => Array
                (
                  [Date] => 2017-07-25 16:17:48
                  [Author] => WooCommerce
                  [Content] => Order exported to XML and successfully downloaded.
                )

              [1] => Array
                (
                  [Date] => 2017-07-25 14:57:25
                  [Author] => WooCommerce
                  [Content] => Order status changed from Pending payment to Processing.
                )

              [2] => Array
                (
                  [Date] => 2017-07-25 14:57:25
                  [Author] => WooCommerce
                  [Content] => Tarp (#478) stock reduced from 118.5 to 82.5.
                )

              [3] => Array
                (
                  [Date] => 2017-07-25 14:57:25
                  [Author] => WooCommerce
                  [Content] => Bogus is always approved 😎
                )

            )

        )

    )

)

)

Potentially a check in this bit to see if $child_element_value is an array before we loop it / recursively call the function?