Fix Zero Length Packet bug

[jcard0na]

To determine if a Zero-Length Packet needs to be sent, we check if data_reminder is greater than zero at the end of a data transfer. Before this fix, pack_csw() resets data_remainder to CommandStatusWrapper::BYTES before checking it. This results in thinking that there was still data to be sent and therefore sending an unnecessary ZLP before the command response. This causes problems with MacOS Read(10) commands.

Fix by checking data_remainder before it is overwritten.