fix an AttributeError

'AnonymousUser' object has no attribute 'email'

tendenci/apps/events/forms.py

@@ -2454,7 +2454,7 @@ def _clean_form(self, form):
             if not get_setting('module', 'events', 'canregisteragain'):
                 # check if this user can register
                 if not self.user.is_superuser:
-                    if self.user.email.lower() != email.lower():
+                    if self.user.is_authenticated and self.user.email.lower() != email.lower():
                         raise forms.ValidationError(_(f"{email} is NOT your email address."))       
 
                 # check if this email address is already used