Catch no-op on updating guardian.

ticdesk_events/views.py

@@ -7,6 +7,7 @@ from django.urls import reverse
 from django.utils.translation import ugettext as _
 from django.shortcuts import redirect, render
 from django_tables2 import RequestConfig
+from ldap import INVALID_SYNTAX
 
 from .forms import EventFeedbackForm, EventRegisterForm
 from .models import TeckidsProject, Voucher
@@ -104,7 +105,11 @@ def register_event(request, cn):
                     # Either mail or mobile matches - update both and link
                     guardian.mail = register_form.cleaned_data['guardian_mail']
                     guardian.mobile = register_form.cleaned_data['guardian_mobile']
-                    guardian.save()
+                    try:
+                        guardian.save()
+                    except INVALID_SYNTAX:
+                        # Uncritical because we hit a no-op
+                        pass
 
                     if guardian.dn not in current_person.guardians:
                         current_person.guardians.append(guardian.dn)