Fix events registration update form

Closes #408 (closed)

Before:

1. Open event page
2. Register for event
3. Enter information in the information fields
4. Save
5. Open the same event page
6. Click update registration
7. Notice that the fields are empty

After:

1. Open event page
2. Register for event
3. Enter information in the information fields
4. Save
5. Open the same event page
6. Click update registration
7. Notice that the fields are not empty