add fallback for config failure

[art0007i]

idk if this is a good idea but I hate it when my mods don't load because the config files saved incorrectly

(maybe I should stop spamming alt+f4 to quit the game which crashes it during the exit procedure, so that the config files don't corrupt in the first place)

[zkxs]

This won't actually solve the problem which is causing configs to get corrupted. More details on that in #97.

The effect of this PR would be that if the top-level map fails to deserialize we'd back up the corrupted config and make a fresh one... that's probably fine, and I think it's a good thing to do versus forcing the user to go hunt around their filesystem to manually delete the corrupted file. So you've got my approval.

[XDelta]

I believe that File.Move will throw an exception if the destination path already has a file. IE if consecutive config fails occur or the old failed config wasn't removed after fixing the issue.

[XDelta]

Either add an overwriting bit or write a unique filename to avoid. Don't have an overwrite option on File.Move until like .Net Core 3.