[Payments] Fix bug in shipping option selection.

components/payments/content/payment_request_spec.cc

Index: components/payments/content/payment_request_spec.cc
diff --git a/components/payments/content/payment_request_spec.cc b/components/payments/content/payment_request_spec.cc
index a3e8322571d6c762b967b06971c3d7a6fda8bb95..bec17e27c30289c3bf12b8a92d23a2122d1c1e19 100644
--- a/components/payments/content/payment_request_spec.cc
+++ b/components/payments/content/payment_request_spec.cc
@@ -178,6 +178,10 @@ void PaymentRequestSpec::UpdateSelectedShippingOption() {
       });
   if (selected_shipping_option_it != details().shipping_options.rend()) {
     selected_shipping_option_ = selected_shipping_option_it->get();
+  } else {
+    // It's possible that there is no selected shipping option.
+    // TODO(crbug.com/710004): Show an error in this case.
+    selected_shipping_option_ = nullptr;
   }
 }