check for connectedness twice

fixes #2708

source

@@ -55747,7 +55747,9 @@ fur
      <code data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true and the <code
      data-x="dom-Event-cancelable">cancelable</code> attribute initialized to true.</p></li>
 
-     <li><p>If <var>continue</var> is false, then abort these steps.
+     <li><p>If <var>continue</var> is false, then return.</p></li>
+
+     <li><p>If <var>form</var> <span>cannot navigate</span>, then return.</p></li>
     </ol>
 
    <!-- if you add any steps between the "lock" and "unlock" lines, make sure to update the step