Fix registration editing organiser non member

Ghost User
2019-03-27T20:33:33+01:00

Closes #839

#### Previous behaviour
Steps to reproduce:

1. Create two non-members in an event registration
2. Mark one as paid & refresh
3. Status moved back

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

1. Create two non-members in an event registration
2. Mark one as paid & refresh
3. Works