fix for invalid parquet (#849)

delete invalid parquets where file size is less than 
the length of the parquet footer

Fixes: #848

server/src/storage/staging.rs

@@ -280,7 +280,7 @@ pub fn convert_disk_files_to_parquet(
  }
 
  writer.close()?;
- if parquet_file.metadata().unwrap().len() == 0 {
+ if parquet_file.metadata().unwrap().len() < parquet::file::FOOTER_SIZE as u64 {
  log::error!(
  "Invalid parquet file {:?} detected for stream {}, removing it",
  &parquet_path,