Do the principle of neutrality and Article 90 of Council Directive 2006/112/EC of 28 November 2006 preclude national legislation such as Article 78(11) of the Código do Imposto sobre o Valor Acrescentado (Value Added Tax Code), which is interpreted to the effect that the tax may not be adjusted, in the event of non-payment, before the purchaser of the goods or service, being a taxable person, has been notified of the cancellation of the tax for the purposes of rectifying the deduction initially made?