[WebUI] Sidebar: fix error for lazy init

When sidebar is hidden at WebUI startup, header isn't created yet.

Signed-off-by: Xuefer H <xuefer@gmail.com>
Closes: https://github.com/deluge-torrent/deluge/pull/419

deluge/ui/web/js/deluge-all/Sidebar.js

@@ -60,6 +60,7 @@ Deluge.Sidebar = Ext.extend(Ext.Panel, {
         this.doLayout();
         this.panels[filter] = panel;
 
+        if (panel.header) {
             panel.header.on('click', function (header) {
                 if (!deluge.config.sidebar_multiple_filters) {
                     deluge.ui.update();
@@ -68,6 +69,7 @@ Deluge.Sidebar = Ext.extend(Ext.Panel, {
                     panel.list.select(0);
                 }
             });
+        }
         this.fireEvent('filtercreate', this, panel);
 
         panel.updateStates(states);