[FIX] sale_loyalty_criteria_order_based: Do not evaluate False domain

In case a promotion is created without defining any domain on the UI,
an error message 'Invalid domain on rule' would appear.

Avoiding  evaluation of the field if its value is Falsish removes the
error.

sale_loyalty_criteria_order_based/models/loyalty_rule.py

@@ -18,6 +18,8 @@ class LoyaltyRule(models.Model):
     def _constrain_rule_order_domain(self):
         model = self.env["sale.order"]
         for rule in self:
+            if not rule.rule_order_domain:
+                continue
             try:
                 domain = ast.literal_eval(rule.rule_order_domain)
                 # Ensuring that domain is valid for sale.order