[BUGFIX] retry transfering with lower size for any HTTP error code

When a timeout is too low compared to sent size, server will return a 500 error.
Jirafeau retry to send again but do not try to reduce chunk size.

This patch will make Jiarfeau split in half it's sent size each an error occurs.

ref #273

Signed-off-by: Jerome Jutteau <jerome@jutteau.fr>