fix: complete() returns rejected promise (#732)

The current spec text read as if calling complete() twice would caused
the interface to close down based on the second call.

This just returns a rejected promise if the completeCalled is `true`.

Author: marcoscaceres

index.html

@@ -3490,25 +3490,26 @@ 
           arguments.
         p>
         <p data-tests="payment-response/complete-method-manual.https.html">
-          The <a>complete(result)a> method MUST act as follows:
+          The <a><code>complete(<var>resultvar>)code>a> method MUST act
+          as follows:
         p>
         <ol class="algorithm">
           <li>Let <var>responsevar> be the <a>context objecta>.
           li>
+          <li>If <var>responsevar>.<a>[[\complete]]a> is true, return <a>a
+          promise rejected witha> an "<a>InvalidStateErrora>"
+          <a>DOMExceptiona>.
+          li>
           <li>Let <var>promisevar> be <a>a new promisea>.
           li>
-          <li>If <var>responsevar>.<a>[[\complete]]a> is true, reject <var>
-            promisevar> with an "<a>InvalidStateErrora>"
-            <a>DOMExceptiona>.
+          <li>Set <var>responsevar>.<a>[[\complete]]a> to true.
           li>
           <li data-tests=
           "payment-request/payment-response/retry-method-manual.https.html">If
           <var>responsevar>.<a>[[\retryPromise]]a> is not null, reject
           <var>promisevar> with an "<a>InvalidStateErrora>"
           <a>DOMExceptiona>.
           li>
-          <li>Otherwise, set <var>responsevar>.<a>[[\complete]]a> to true.
-          li>
           <li>Return <var>promisevar> and perform the remaining steps <a>in
           parallela>.
           li>