Don't queue up more than a single save command

[huntfx]

If the saving is set to 5 seconds for example, by the time one save is finished, there may have been another two queued up. This causes the script to get further and further behind where it'll never get a chance to catch up.

[huntfx]

I think I've got it working. The next save is now calculated from the end of the saving, not the start. The background thread needs to send back a notification for this to happen.