message: Don't treat Unobtainable as a failure if in_flight != 0
diff: @@ -154,6 +154,12 @@ impl LeapActivity {
  best_available: Box::new(best_available),
  from_peers,
  },
  + // `Unobtainable` means we couldn't download it from any peer so far - don't treat it
  + // as a failure if there are still requests in flight
  + Err(LeapActivityError::Unobtainable(_, _)) if in_flight > 0 => LeapStatus::Awaiting {
  + sync_leap_identifier,
  + in_flight,
  + },
  Err(error) => LeapStatus::Failed {
  sync_leap_identifier,
  from_peers: vec![],
  