Check there is a browsing context in document.open()'s abort step

This was missed in #3999.

Author: TimothyGu

source

@@ -91022,7 +91022,8 @@ document.body.appendChild(frame)</code></pre>
    </li>
 
    <li>
-    <p>If there is an existing attempt to <span>navigate</span> <var>document</var>'s <span
+    <p>If <var>document</var> has a <span data-x="concept-document-bc">browsing context</span> and
+    there is an existing attempt to <span>navigate</span> <var>document</var>'s <span
     data-x="concept-document-bc">browsing context</span>, then <span>stop document loading</span>
     given <var>document</var>.</p>