title: boto3 django transfer.upload_file is breaking image, incomplete transfer
body: <p>I am using boto3 library for transferring user uploaded image on my web application to S3 bucket, i am using transfer.upload_file but strangely part of the image gets vanished in uploaded file, though file seems perfect on instance but not in S3 bucket, any help would be really great. </p>
  
  <p>I am uploading file to local server via : </p>
  
  <pre><code>fpath = settings.STATIC_ROOT + '/temp/' + self.fileObj.name
  filename, file_extension = os.path.splitext(fpath) newName = Encrypt(str(int(time.time())) + filename).encrypt() + file_extension 
  destination = open(fpath, 'wb+')
  for chunk in self.fileObj.chunks(): 
       destination.write(chunk) 
  </code></pre>
  
  <p>then to s3 via client </p>
  
  <pre><code> boto3.client('s3',S3_REGION) transfer = S3Transfer(client) 
   transfer.upload_file( fpath, S3_STORAGE_BUCKET_NAME,self.folder+'/'+newName, extra_args={'ACL': 'public-read', 'ContentType':mime_type} )
  </code></pre>