Fix saving pizza event if notification already exists

Ghost User
2019-05-22T22:34:03+02:00

#### Previous behaviour
Steps to reproduce:

1. Create a pizza event with notification
2. Edit said event and save
3. :fire:

#### New behaviour
Steps to validate that it works:

1. Create a pizza event with notification
2. Edit said event and save
3. :white\_check\_mark: