[FIX] base: default rate

We set the default rate to be 1.0 instead of 0.0, since a rate of 0.0
doesn't make sense.

Partial backport of 298491597c

opw-1949866

closes odoo/odoo#31866

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

odoo/addons/base/res/res_currency.py

@@ -206,7 +206,7 @@ class CurrencyRate(models.Model):
 
     name = fields.Datetime(string='Date', required=True, index=True,
                            default=lambda self: fields.Date.today() + ' 00:00:00')
-    rate = fields.Float(digits=(12, 6), help='The rate of the currency to the currency of rate 1')
+    rate = fields.Float(digits=(12, 6), default=1.0, help='The rate of the currency to the currency of rate 1')
     currency_id = fields.Many2one('res.currency', string='Currency', readonly=True)
     company_id = fields.Many2one('res.company', string='Company',
                                  default=lambda self: self.env.user.company_id)