Sanitize trailing ? when stripping analytics parameters from URL

Safari doesn't remove the ? from a URL when setting `url.search = ''`
which results in links not correctly applying `:visited`.

For example, before this change:
https://www.reddit.com/?utm_foo=bar -> https://www.reddit.com/?
and links to https://www.reddit.com/ don't render as :visited

After this change,
https://www.reddit.com/?utm_foo=bar -> https://www.reddit.com/
and links to https://www.reddit.com/ are properly empurpled.
Additionally, hash is preserved:
https://www.reddit.com/?utm_foo=bar&baz=qux#hoopla -> https://www.reddit.com/?baz=qux#hoopla

r2/r2/public/static/js/analytics.js

@@ -329,6 +329,10 @@ r.analytics = {
       var a = document.createElement('a');
       a.href = window.location.href;
       a.search = $.param(strippedParams);
+      if (!a.search) {
+        // Safari leaves a trailing ? when search is empty
+        a.href = a.href.replace(/\?(#.+)?$/, a.hash);
+      }
 
       window.history.replaceState({}, document.title, a.href);
     }