message: rafs/v6: fix panic when making image with xattr having non-utf8 chars
  Not all the charactors of os string can be converted to rust utf-8 string.
  Luckily, thos essential namespaces names can be converted.
diff: @@ -1615,11 +1615,7 @@ impl RafsXAttrs {
  fn match_prefix(key: &OsStr) -> Result<(u8, usize)> {
  let pos = RAFSV6_XATTR_TYPES
  .iter()
  - .position(|x| {
  - key.to_str()
  - .expect("failed to convert osstr to str")
  - .starts_with(x.prefix)
  - })
  + .position(|x| key.to_string_lossy().starts_with(x.prefix))
  .ok_or_else(|| einval!(format!("xattr prefix {:?} is not valid", key)))?;
  Ok((
  RAFSV6_XATTR_TYPES[pos].index,
  