[FIX] l10n_it_edi: use customer country for Nazione field

Steps to reproduce:
- Install Accounting, l10n_it_edi and Contacts
- Switch to an Italian company (e.g. IT Company)
- Go to Contacts
- Create an EU contact with "/" or "NA" as VAT
(e.g. a Germnan contact with a full address)
- Create an invoice:
  * Customer: [the created contact]
  * Product: [any]
- Confirm the invoice
- Process the electronic invoice
- Check the generated electronic invoice

Issue:
1) The country of customer is first computed from his VAT number and
a fallback is made on his country.
It should be the opposite.
2) In the XML, the "IdFiscaleIVA" section is set for customer with "/" (or "NA")
as "IdPaese", but it should not because customer doesn't have a VAT number.
If the XML is sent for validation, it is rejected because of that.

Solution:
1) Backport of odoo#164950
2) Add a condition on "IdFiscaleIVA" node as it is done from saas-16.4

opw-3889051

closes odoo#165253

Signed-off-by: Wala Gauthier (gawa) <gawa@odoo.com>

addons/l10n_it_edi/data/invoice_it_template.xml

@@ -99,7 +99,7 @@
         </RappresentanteFiscale>
         <CessionarioCommittente>
             <DatiAnagrafici>
-                <IdFiscaleIVA>
+                <IdFiscaleIVA t-if="buyer_info['vat']">
                     <IdPaese t-out="buyer_info['country_code']"/>
                     <IdCodice t-out="buyer_info['vat']"/>
                 </IdFiscaleIVA>

addons/l10n_it_edi/models/account_invoice.py

@@ -221,45 +221,35 @@ def get_vat_values(partner):
                 If there is no VAT and no Codice Fiscale, the invoice is not even exported, so this case is not handled.
 
                 Country:
-                First, try and deduct the country from the VAT number.
-                If not, take the country directly from the partner.
-                If there's a codice fiscale, the country is 'IT'.
+                First, take the country configured on the partner.
+                If there's a codice fiscale and no country, the country is 'IT'.
             """
             europe = self.env.ref('base.europe', raise_if_not_found=False)
             in_eu = europe and partner.country_id and partner.country_id in europe.country_ids
             is_sm = partner.country_code == 'SM'
 
             normalized_vat = partner.vat
-            normalized_country = False
+            normalized_country = partner.country_code
             if partner.vat:
                 normalized_vat = partner.vat.replace(' ', '')
                 if in_eu:
-                    # If there is no country-code prefix, it's domestic to Italy
-                    if normalized_vat[:2].isdecimal():
-                        normalized_country = 'IT'
                     # If the partner is from the EU, the country-code prefix of the VAT must be taken away
-                    else:
-                        normalized_country = normalized_vat[:2].upper()
+                    if not normalized_vat[:2].isdecimal():
                         normalized_vat = normalized_vat[2:]
                 # If customer is from San Marino
                 elif is_sm:
-                    normalized_country = 'SM'
                     normalized_vat = normalized_vat if normalized_vat[:2].isdecimal() else normalized_vat[2:]
                 # The Tax Agency arbitrarily decided that non-EU VAT are not interesting,
                 # so this default code is used instead
                 # Detect the country code from the partner country instead
                 else:
                     normalized_vat = 'OO99999999999'
 
-            if not normalized_country:
-                if partner.country_id:
-                    normalized_country = partner.country_id.code
-                # If it has a codice fiscale (and no country), it's an Italian partner
-                elif partner.l10n_it_codice_fiscale:
-                    normalized_country = 'IT'
+            # If it has a codice fiscale (and no country), it's an Italian partner
+            if not normalized_country and partner.l10n_it_codice_fiscale:
+                normalized_country = 'IT'
             elif not partner.vat and partner.country_id and partner.country_id.code != 'IT':
                 normalized_vat = '0000000'
-                normalized_country = partner.country_id.code
 
             return {
                 'vat': normalized_vat,