message: Polish code to clarify meaning
  This preserves the same behavior, but the previous code looked like it might
  loop, but in fact never did.
diff: @@ -504,14 +504,12 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
  // Drain the client fully
  for i in 0..tokens {
  - while let Err(e) = client.acquire_raw() {
  - anyhow::bail!(
  - "failed to fully drain {}/{} token from jobserver at startup: {:?}",
  - i,
  - tokens,
  - e,
  - );
  - }
  + client.acquire_raw().chain_err(|| {
  + format!(
  + "failed to fully drain {}/{} token from jobserver at startup",
  + i, tokens,
  + )
  + })?;
  }
  Ok(client)
  