Cannot fill in field for guest registration

bug

Closes #925 (closed)

Previous behaviour

Steps to reproduce:

1. create an event with registration fields
2. add a registration with a name
3. try to change the field
4. nothings happens

New behaviour

Steps to validate that it works:

1. create an event with registration fields
2. add a registration with a name
3. try to change the field
4. it is changed