Do not add chunk data for empty ByteBuffer

Motivation and Context

When doing S3 PutObject with flexible checksums with S3AsyncClient, the ChecksumCalculatingAsyncRequestBody adds chunk headers and trailers to each chunk. We should skip this if there is a non-final empty chunk of length 0, as it causes an error to be thrown

S3Exception: You did not provide the number of bytes specified by the Content-Length HTTP header

Modifications

In onNext(), return the ByteBuffer as is, if it is empty and non-final chunk

Testing

added unit tests, performed one-off integ tests

Screenshots (if appropriate)

Types of changes

[x] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)

Checklist

[ ] I have read the CONTRIBUTING document
[ ] Local run of mvn install succeeds
[ ] My code follows the code style of this project
[ ] My change requires a change to the Javadoc documentation
[ ] I have updated the Javadoc documentation accordingly
[ ] I have added tests to cover my changes
[ ] All new and existing tests passed
[ ] I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
[ ] My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

[ ] I confirm that this pull request can be released under the Apache 2 license

aws / aws-sdk-java-v2

Do not add chunk data for empty ByteBuffer #5320