[FIX] crm: setting alias_prefix easy reinited

The previous code when "Manually Assignation of Incoming Emails" sale
config was set always set the alias prefix to "info" even if another
value had been previously saved.

opw-745174
closes #17305

addons/crm/models/res_config.py

@@ -59,7 +59,10 @@ class CRMSettings(models.TransientModel):
 
     @api.onchange('default_generate_lead_from_alias')
     def _onchange_default_generate_lead_from_alias(self):
-        self.alias_prefix = 'info' if self.default_generate_lead_from_alias else False
+        if self.default_generate_lead_from_alias:
+            self.alias_prefix = self.alias_prefix or 'info'
+        else:
+            self.alias_prefix = False
 
     @api.model
     def get_default_alias_prefix(self, fields):