appenlight client: do not set empty server urls

rhodecode/templates/base/root.html

@@ -69,7 +69,9 b" c.template_context['visual']['default_re"
             var APPENLIGHT = {
               enabled: ${'true' if getattr(c, 'appenlight_enabled', False) else 'false'},
               key: '${getattr(c, "appenlight_api_public_key", "")}',
+              % if getattr(c, 'appenlight_server_url', None):
               serverUrl: '${getattr(c, "appenlight_server_url", "")}',
+              % endif
               requestInfo: {
               % if getattr(c, 'rhodecode_user', None):
                   ip: '${c.rhodecode_user.ip_addr}',