message: Fixes after feedback
diff: @@ -143,7 +143,7 @@ pub extern "system" fn librustzcash_init_zksnark_params(
  let output_path = Path::new(OsStr::from_bytes(unsafe {
  slice::from_raw_parts(output_path, output_path_len)
  }));
  - let sprout_path = if sprout_path.is_null() && sprout_path_len == 0 {
  + let sprout_path = if sprout_path.is_null() {
  None
  } else {
  Some(Path::new(OsStr::from_bytes(unsafe {
  @@ -178,7 +178,7 @@ pub extern "system" fn librustzcash_init_zksnark_params(
  OsString::from_wide(unsafe { slice::from_raw_parts(spend_path, spend_path_len) });
  let output_path =
  OsString::from_wide(unsafe { slice::from_raw_parts(output_path, output_path_len) });
  - let sprout_path = if sprout_path.is_null() && sprout_path_len == 0 {
  + let sprout_path = if sprout_path.is_null() {
  None
  } else {
  Some(OsStr::from_wide(unsafe {
  @@ -215,7 +215,7 @@ fn init_zksnark_params(
  .to_str()
  .expect("hash should be a valid string");
  - let sprout_hash_option = if sprout_path.is_none() {
  + let sprout_hash = if sprout_path.is_none() {
  None
  } else {
  Some(
  @@ -232,7 +232,7 @@ fn init_zksnark_params(
  output_path,
  output_hash,
  sprout_path,
  - sprout_hash_option,
  + sprout_hash,
  );
  // Caller is responsible for calling this function once, so
  