Fix only sending partial file contents on retries

ia-upload-stream

@@ -209,6 +209,7 @@ def upload(item, filename, metadata, *, iaConfigFile = None, partSize = 100*1024
 			if attempt == tries:
 				raise UploadError(f'Got {err} from IA S3 on uploading part {partNumber}', r = r, uploadId = uploadId, parts = parts)
 			time.sleep(sleepTime)
+			data.seek(0)
 		logger.info(f'Upload OK, ETag: {r.headers["ETag"]}')
 		parts.append((partNumber, r.headers['ETag']))