agendas: fix event name decoding returned by vobject (#19060)

chrono/agendas/models.py

@@ -429,7 +429,9 @@ class Desk(models.Model):
         with transaction.atomic():
             for vevent in parsed.contents['vevent']:
                 event = {}
-                summary = unicode(vevent.contents['summary'][0].value, 'utf-8')
+                summary = vevent.contents['summary'][0].value
+                if not isinstance(summary, unicode):
+                    summary = unicode(summary, 'utf-8')
                 if 'rrule' in vevent.contents:
                     raise ICSError(_('Recurrent events are not handled.'))
                 try: