Handle I/O errors so that the data file is not wiped

[VincentCordobes]

Today, as I was running out of disk space, trackie stop failed with the no space left error. But the data file was already truncated and the data is no more.

An idea would be to write the state to a different file first and, if it succeeds only, replace the data file.

[beatbrot]

Sounds good! Maybe there is also some existing OS API for something like this?

Unfortunately, I don't know when I'll find time to implement this...