authn: Only lookup settings from DB if they are really used.

When computing the form defaults only query the DB if we
need the value from DB.

rhodecode/authentication/views.py

@@ -59,9 +59,9 b' class AuthnPluginViewBase(object):'
         # Compute default values for the form. Priority is:
         # 1. Passed to this method 2. DB value 3. Schema default
         for node in schema:
-            value = self.plugin.get_setting_by_name(
+            if node.name not in defaults:
+                defaults[node.name] = self.plugin.get_setting_by_name(
                 node.name, node.default)
-            defaults.setdefault(node.name, value)
 
         template_context = {
             'defaults': defaults,