Fix removal of Firebase Admin SDK error

Ghost User
2019-10-19T09:21:52+02:00

Closes #940

#### Previous behaviour
Steps to reproduce:

1. Send a push message that triggers an error
2. The message is not marked as sent and hard crash

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

1. Send a push message that triggers an error
2. The message is marked as sent and everything works