[REF] account: externilize fiscal year validation

create _validate_fiscalyear() method in res.company
so that it is easier to inherit to modify or extend its
functionality.

addons/account/models/company.py

@@ -80,15 +80,20 @@ def reflect_code_digits_change(self, digits):
             account.write({'code': account.code.rstrip('0').ljust(digits, '0')})
 
     @api.multi
-    def write(self, values):
-        #restrict the closing of FY if there are still unposted entries
+    def _validate_fiscalyear(self, values):
         if values.get('fiscalyear_lock_date'):
             nb_draft_entries = self.env['account.move'].search([
                 ('company_id', 'in', [c.id for c in self]),
                 ('state', '=', 'draft'),
                 ('date', '<=', values['fiscalyear_lock_date'])])
             if nb_draft_entries:
                 raise ValidationError(_('There are still unposted entries in the period you want to lock. You should either post or delete them.'))
+
+    @api.multi
+    def write(self, values):
+        #restrict the closing of FY if there are still unposted entries
+        self._validate_fiscalyear(values)
+
         # Reflect the change on accounts
         for company in self:
             digits = values.get('accounts_code_digits') or company.accounts_code_digits