Bug: sent payments do not show up in flow report

[C-Otto]

Related to #14

I paid an invoice to pay for some service. I can't see the amount in the flow report for the channel that was used to pay the invoice. I expect this to be a separate entry.

To reproduce
Let someone else create an invoice. Pay invoice. Look at flow report of channel that was used to send payment that settled the invoice.

Expected behavior
The sent amount is mentioned in the flow report.