hgweb: evaluate the "default" value as template

Strictly speaking, everything in the map file is a template. So let's not
take out an unparsed template string.

mercurial/hgweb/hgweb_mod.py

@@ -386,7 +386,7 b' class hgweb(object):'
                 self.check_perm(rctx, req, None)
 
             if cmd == '':
-                req.qsparams['cmd'] = rctx.tmpl.cache['default']
+                req.qsparams['cmd'] = rctx.tmpl.render('default', {})
                 cmd = req.qsparams['cmd']
 
             # Don't enable caching if using a CSP nonce because then it wouldn't