[FIX] event: print registrations without name

Before this commit, trying to print a registration without a name
specified (not required), was failing

Fixes odoo/odoo#38564

Replace and closes odoo/odoo#38582
Courtesy of Swapnesh Shah

closes odoo/odoo#38767

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

addons/event/report/event_event_reports.xml

@@ -25,7 +25,7 @@
         name="event.event_registration_report_template_badge"
         file="event.event_registration_report_template_badge"
         paperformat="event.paperformat_euro_lowmargin"
-        print_report_name="'Registration Event - %s' % (object.name).replace('/','')"
+        print_report_name="'Registration Event - %s' % (object.name or 'Attendee').replace('/','')"
     />
 
      <report