If client_id is invalid and req.query.allowed = false, please throw InvalidClientError instead of AccessDeniedError

[chaudhryjunaid]

Oauth recommends not redirecting to redirect_uri in case of invalid client. However, in case of req.query.allowed === 'false', client is not checked at all and an AccessDeniedError is thrown immediately. In AccessDeniedError I want to redirect to redirect uri but oauth2-server has not checked client uri at all. Kindly change the order of checking and throwing errors. InvalidClientError is a higher priority error than AccessDeniedError.