Fix panning sounds after scrolling.

tests/browser-linked-headings.html

@@ -11,4 +11,8 @@
 <h4>Ordinary heading</h4>
 <h5>Choose: <a href="#first">First link</a> and <a href="#second">Second link</a></h5>
 <p id="first">First destination</p><p id="second">Second destination</p>
+<h6 style="margin-top: 1200px"><a href="#sound-first">Offscreen first topic</a></h6>
+<p id="sound-first">First sound destination</p>
+<h6 style="margin-top: 1200px"><a href="#sound-second">Offscreen second topic</a></h6>
+<p id="sound-second">Second sound destination</p>
 </body></html>