[FIX] _witholding: restore date for partner aliquot

revertimos esto 5fb0ba2
para tener de nuevo esto que es necesario para que la factura calcule bien bc5eba3

closes #848

Signed-off-by: mem-adhoc <mem@adhoc.com.ar>

l10n_ar_account_withholding/models/account_tax.py

@@ -258,6 +258,9 @@ def _compute_amount(
             self, base_amount, price_unit, quantity=1.0, product=None, partner=None, fixed_multiplicator=1):
         if self.amount_type == 'partner_tax':
             date = self._context.get('invoice_date', fields.Date.context_today(self))
+
+            if not date:
+                date = fields.Date.context_today(self)
             partner = partner and partner.sudo()
             return base_amount * self.sudo().get_partner_alicuota_percepcion(partner, date)
         else: