upgrader: Login banner

Don't crash when login-banner page doesn't exist yet.

include/class.page.php

@@ -237,6 +237,9 @@ class Page extends VerySimpleModel {
         catch (DoesNotExist $ex) {
             return null;
         }
+        catch (InconsistentModelException $ex) {
+            return null;
+        }
     }
 
     function update($vars, &$errors) {