[FIX] account: included tax with fiscal position

When creating an invoice with a fiscal position(fp) which maps an included tax(itax)
to an excluded tax(etax). Each invoice line mapped by fp must recompute its unit price
to substract the included tax.
Inspired from 503820a

Closes #9811

opw:658109

addons/account/account_invoice.py

@@ -1347,13 +1347,16 @@ class account_invoice_line(models.Model):
             if product.description_purchase:
                 values['name'] += '\n' + product.description_purchase
 
-        taxes = fpos.map_tax(taxes)
-        values['invoice_line_tax_id'] = taxes.ids
+        fp_taxes = fpos.map_tax(taxes)
+        values['invoice_line_tax_id'] = fp_taxes.ids
 
         if type in ('in_invoice', 'in_refund'):
-            values['price_unit'] = price_unit or product.standard_price
+            if price_unit and price_unit != product.standard_price:
+                values['price_unit'] = price_unit
+            else:
+                values['price_unit'] = self.env['account.tax']._fix_tax_included_price(product.standard_price, taxes, fp_taxes.ids)
         else:
-            values['price_unit'] = product.lst_price
+            values['price_unit'] = self.env['account.tax']._fix_tax_included_price(product.lst_price, taxes, fp_taxes.ids)
 
         values['uos_id'] = product.uom_id.id
         if uom_id:
@@ -1368,8 +1371,6 @@ class account_invoice_line(models.Model):
 
         if company and currency:
             if company.currency_id != currency:
-                if type in ('in_invoice', 'in_refund'):
-                    values['price_unit'] = product.standard_price
                 values['price_unit'] = values['price_unit'] * currency.rate
 
             if values['uos_id'] and values['uos_id'] != product.uom_id.id: