Quoted 0 fee, payment ended up with a fee

[wbobeirne]

Description

When sending a lightning payment, I was showed zero for the fee. After sending it, I ended up with a 31 satoshi fee.

Screenshot and/or logs if applicable

The relevant logs at the time seem to indicate maybe multiple paths were tried, maybe the 0 fee route quoted didn't pan out when it tried, and ended up using a longer route?

2019-10-17 02:36:05.643 [ERR] RPCS: [/lnrpc.Lightning/QueryRoutes]: unable to find a path to destination
2019-10-17 02:36:09.021 [INF] SRVR: Adding preimage=22685e24dd712c84410881544e05634639a1dddd3719e3af656257ad564fd695 to witness cache