Change Location/<a>/<area>'s port setter

Setting it to the empty string should set the underlying port concept
to null. See web-platform-tests/wpt#4101 for
test changes and whatwg/url#113 for the change
to the URL Standard.

source

@@ -21918,7 +21918,10 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
    data-x="concept-url-scheme">scheme</span> is "<code data-x="">file</code>", terminate these
    steps.</p></li>
 
-   <li><p><span data-x="basic url parser">Basic URL parse</span> the given value, with
+   <li><p>If the given value is the empty string, then set <var>url</var>'s <span
+   data-x="concept-url-port">port</span> to null.</p></li>
+
+   <li><p>Otherwise, <span data-x="basic url parser">basic URL parse</span> the given value, with
    <var>url</var> as <var>url</var> and <span>port state</span> as <var>state
    override</var>.</p></li>
 
@@ -80586,7 +80589,10 @@ State: &lt;OUTPUT NAME=I>1&lt;/OUTPUT> &lt;INPUT VALUE="Increment" TYPE=BUTTON O
    data-x="concept-url-scheme">scheme</span> is "<code data-x="">file</code>", terminate these
    steps.</p></li>
 
-   <li><p><span data-x="basic url parser">Basic URL parse</span> the given value, with
+   <li><p>If the given value is the empty string, then set <var>copyURL</var>'s <span
+   data-x="concept-url-port">port</span> to null.</p></li>
+
+   <li><p>Otherwise, <span data-x="basic url parser">basic URL parse</span> the given value, with
    <var>copyURL</var> as <var>url</var> and <span>port state</span> as <var>state
    override</var>.</p></li>