Version:
s3cmd version 2.0.2

How to reproduce the issue:
Assuming s3://some_bucket/some_file has been already downloaded to the current path, executing s3cmd get s3://some_bucket/some_file . --continue would generate an error: ERROR: S3 error: 416 (InvalidRange): The requested range is not satisfiable

Expected behavior:
No error shall appear if the file is already fully transferred.

A probably common use case:
When trying to download a directory and the transmission is unexpectedly interrupted, one may want to try s3cmd get s3://some_bucket/some_path some_local_path --recursive --skip-existing --continue to recover the progress.