message: Invert map and filter_map usage
  This changes the code to use filter_map and map in a different order to
  reduce the amount of line noise.  It's slightly less clear, but a lot
  less weird.
diff: @@ -611,14 +611,10 @@ impl LossRecovery {
  }
  PNSpace::iter()
  - .map(|spc| (*spc, self.spaces[*spc].earliest_sent_time()))
  - .filter_map(|(spc, time)| {
  - // None is ordered less than Some(_). Bad. Filter them out.
  - if let Some(time) = time {
  - Some((spc, time))
  - } else {
  - None
  - }
  + .filter_map(|&spc| {
  + self.spaces[spc]
  + .earliest_sent_time()
  + .map(|time| (spc, time))
  })
  .min_by_key(|&(_, time)| time)
  .map(|(spc, val)| (spc, val + self.loss_delay()))
  