message: storage: implement FileCacheEntry::is_all_data_ready()
  Implement FileCacheEntry::is_all_data_ready() to query whether all
  chunk data is ready.
diff: @@ -217,7 +217,11 @@ impl BlobObject for FileCacheEntry {
  }
  fn is_all_data_ready(&self) -> bool {
  - todo!()
  + if let Some(b) = self.chunk_map.as_bitmap() {
  + b.is_bitmap_all_ready()
  + } else {
  + false
  + }
  }
  fn fetch(&self, offset: u64, size: u64) -> Result<usize> {
  