[FIX] auth_ldap: avoid to try twice the authentication to the ldap server

See #1982

addons/auth_ldap/users_ldap.py

@@ -251,6 +251,10 @@ class users(osv.osv):
             return user_id
         registry = RegistryManager.get(db)
         with registry.cursor() as cr:
+            cr.execute("SELECT id, active FROM res_users WHERE lower(login)=%s", (login,))
+            res = cr.fetchone()
+            if res:
+                return False
             ldap_obj = registry.get('res.company.ldap')
             for conf in ldap_obj.get_ldap_dicts(cr):
                 entry = ldap_obj.authenticate(conf, login, password)