[FIX] website_event_track: do not reset url when changing partner

When changing customer on a sponsor, update website only if defined on the
partner. Otherwise you may reset valid website value with a void value which
is not what people expect. Partner gives a default value but fields are not
completely synchronized.

Follow up of 532c2b44ff

closes odoo/odoo#54867

X-original-commit: 2a47d91703e379d905f457e56482e6e152b4da15
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/website_event_track/models/event_sponsor.py

@@ -36,7 +36,8 @@ class Sponsor(models.Model):
     @api.depends('partner_id')
     def _compute_url(self):
         for sponsor in self:
-            sponsor.url = sponsor.partner_id.website
+            if sponsor.partner_id.website or not sponsor.url:
+                sponsor.url = sponsor.partner_id.website
 
     def _message_get_suggested_recipients(self):
         recipients = super(Sponsor, self)._message_get_suggested_recipients()