Rejected incoming call appears logged 6 times for Africa's Talking channel

[pmallol]

Version 3.3-dev-69e2aac

Preconditions:
The user already has an AfT account
There's an AfT channel configured without a call flow

1. Call AfT channel from a phone
2. Check call logs

Obtained:
No one answers the call.
The rejected incoming call appears logged 6 times with different IDs in verboice with state: "Failed" and Failure information: "No-call-flow. No Incoming Flow Defined."
AfT logs also show 6 entries for the same call.

https://verboice-stg.instedd.org/calls/87743