Align <a>/<area>/Location's pathname getter with the URL Standard

Updates the pathname getter to return the empty string when the URL's path is empty, which mirrors the change in whatwg/url@b087fe2 which in turn fixed whatwg/url#212.

(This was tested as part of the URL Standard change. It is not tested for the Location object as it is not feasible to do so as discussed in the pull request for this change.)

source

@@ -22057,6 +22057,9 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
    <li><p>If <var>url</var>'s <span>cannot-be-a-base-URL flag</span> is set, return the first string
    in <var>url</var>'s <span data-x="concept-url-path">path</span>.</p></li>
 
+   <li><p>If <var>url</var>'s <span data-x="concept-url-path">path</span> is empty, then return the
+   empty string.</p></li>
+
    <li><p>Return "<code data-x="">/</code>", followed by the strings in <var>url</var>'s <span
    data-x="concept-url-path">path</span> (including empty strings), separated from each other by
    "<code data-x="">/</code>".</p></li>
@@ -81112,6 +81115,9 @@ State: &lt;OUTPUT NAME=I>1&lt;/OUTPUT> &lt;INPUT VALUE="Increment" TYPE=BUTTON O
    <li><p>If <var>url</var>'s <span>cannot-be-a-base-URL flag</span> is set, return the first string
    in <var>url</var>'s <span data-x="concept-url-path">path</span>.</p></li>
 
+   <li><p>If <var>url</var>'s <span data-x="concept-url-path">path</span> is empty, then return the
+   empty string.</p></li>
+
    <li><p>Return "<code data-x="">/</code>", followed by the strings in <var>url</var>'s <span
    data-x="concept-url-path">path</span> (including empty strings), separated from each other by
    "<code data-x="">/</code>".</p></li>