FreeSpaceOnDisk type should be int64

[daye-liu]

The error in the FreeSpaceOnDisk type within the ServerState struct of the MainData struct in the GetMainData function! By examining the qBittorrent source code, it was found that it is of type int64, but it was incorrectly defined as uint64 here, leading to the error!

[zze0s]

Hi! That didn't come up during our testing. One would assume disk size wouldn't go below 0, so we went with uint64.

Feel free to PR a fix 👍