fix range calculation in compose_object API (#1416)

Signed-off-by: Bala.FA <[email protected]>

minio/api.py

@@ -1601,13 +1601,11 @@ def compose_object(
  continue
  while size > 0:
  part_number += 1
- start_bytes = offset
- end_bytes = start_bytes + MAX_PART_SIZE
- if size < MAX_PART_SIZE:
- end_bytes = start_bytes + size
+ length = size if size < MAX_PART_SIZE else MAX_PART_SIZE
+ end_bytes = offset + length - 1
  headers_copy = headers.copy()
  headers_copy["x-amz-copy-source-range"] = (
- f"bytes={start_bytes}-{end_bytes}"
+ f"bytes={offset}-{end_bytes}"
  )
  etag, _ = self._upload_part_copy(
  bucket_name,
@@ -1617,8 +1615,8 @@ def compose_object(
  headers_copy,
  )
  total_parts.append(Part(part_number, etag))
- offset = start_bytes
- size -= end_bytes - start_bytes
+ offset += length
+ size -= length
  result = self._complete_multipart_upload(
  bucket_name, object_name, upload_id, total_parts,
  )