Error when app enabled for admins only.

[tomneedham]

Steps to reproduce

1. Enable app for admins only
2. Create announcement

Expected behaviour

Should work fine

Actual behaviour

See this in the log:
{"reqId":"VsPMO6eR4vKeMTZKKvwz","level":3,"time":"2017-06-20T10:13:06+00:00","remoteAddr":"","user":"--","app":"PHP","method":"--","url":"--","message":"Undefined index: announcementcenter at \/Users\/tomneedham\/Projects\/www\/cloud\/apps\/activity\/lib\/Consumer.php#69"}

OC 10.0.3 pre-alpha with announcementcentre enabled for admins only