message: fscache: correctly handle blob_size()
  Originally the file cache subsystem will set the size of cached file
  to the blob size, which breaks fscache's expection. So skip set blob
  file size fo fscache.
diff: @@ -202,17 +202,8 @@ impl FileCacheEntry {
  .backend
  .get_reader(blob_info.blob_id())
  .map_err(|_e| eio!("failed to get blob reader"))?;
  - let blob_size = Self::get_blob_size(&reader, &blob_info)?;
  -
  + let blob_size = blob_info.uncompressed_size();
  let meta = if blob_info.meta_ci_is_valid() {
  - // Set cache file to its expected size.
  - let file_size = file.metadata()?.len();
  - if file_size == 0 {
  - file.set_len(blob_info.uncompressed_size())?;
  - } else {
  - assert_eq!(file_size, blob_info.uncompressed_size());
  - }
  -
  Some(Arc::new(BlobMetaInfo::new(
  &blob_file_path,
  &blob_info,
  