fix handling of returned iterable in s3 file reader
fix handling of returned iterable in s3 file reader

jwittenbach/thunder,j-friedrich/thunder,kunallillaney/thunder,mikarubi/thunder,kcompher/thunder,zhwa/thunder,poolio/thunder,broxtronix/thunder,thunder-project/thunder,j-friedrich/thunder,kcompher/thunder,pearsonlab/thunder,mikarubi/thunder,zhwa/thunder,poolio/thunder,oliverhuangchao/thunder,kunallillaney/thunder,broxtronix/thunder,pearsonlab/thunder,oliverhuangchao/thunder