Fix dialog requestClose() to handle edge case

Dialog requestClose() now directly calls close the dialog if dialog's close watcher is null.

This replaces a previous assert that's wrong.

source

@@ -62087,8 +62087,8 @@ interface <dfn interface>HTMLDialogElement</dfn> : <span>HTMLElement</span> {
    <li><p>If <var>this</var> does not have an <code data-x="attr-dialog-open">open</code>
    attribute, then return.</p></li>
 
-   <li><p><span>Assert</span>: <var>this</var>'s <span data-x="dialog-close-watcher">close
-   watcher</span> is not null.</p></li>
+   <li><p>If <var>this</var>'s <span data-x="dialog-close-watcher">close watcher</span> is null, then
+   <span>close the dialog</span> <span>this</span> with <var>returnValue</var> and return.</p></li>
 
    <li><p>Set <var>dialog</var>'s <span>enable close watcher for <code
    data-x="dom-dialog-requestClose">requestClose()</code></span> to true.</p></li>