recent_topics: Let browser handle the inputs we didn't.

For inputs to recent topics which were unhandled, we return false
so that the browser can handle them.

This also fixes the issue of search box not able input `t` key.

static/js/recent_topics.js

@@ -634,7 +634,7 @@ exports.change_focused_element = function (e, input_key) {
         current_focus_elem.trigger("focus");
     }
 
-    return true;
+    return false;
 };
 
 window.recent_topics = exports;