Gets the currently stored system update hash.

A certain internal NIM state flag must be non-zero, otherwise error 0xE0A0D3F8 is returned. This is the only time this command can return non-zero.

This writes the SystemTitleHash already stored in memory to the command response. This is initially from savedata. When doing SOAP request(s) this data is updated with the latest data from the SOAP response, then the data for this in savedata is updated.