src/client/http_client.rs: append chunks in correct order

We need to wait for response from upload_chunk. After that we can
add the chunk to the index file.

src/api2/admin/datastore/backup/upload_chunk.rs

@@ -96,7 +96,6 @@ fn upload_dynamic_chunk(
 
             let result = result.and_then(|(digest, size)| {
                 env.register_chunk(digest, size)?;
-                env.dynamic_writer_append_chunk(wid, offset, size, &digest)?;
                 Ok(json!(tools::digest_to_hex(&digest)))
             });