message: rustcc should have caught this
diff: @@ -351,12 +351,9 @@ impl SecretAgent {
  // Prepare to encode.
  let mut encoded = Vec::with_capacity(encoded_len);
  - let mut cursor = 0usize;
  let mut add = |v: String| {
  encoded.push(v.len() as u8);
  - cursor += 1;
  encoded.extend_from_slice(v.as_bytes());
  - cursor += v.len();
  };
  // NSS inherited an idiosyncratic API as a result of having implemented NPN
  