do not overwrite config.json while restoring if json syntax error

[vnadot]

Hi,
I just discovered your software, it seems a really nice tool, congrats !
I've noticed that if there is a syntax error in config.json, then lwsm overwrites it with its default value when restoring a config. This behavior seems to me annoying because you can loose your own config (eg the mapping you have defined in WM_CLASS_AND_EXECUTABLE_FILE_MAP) if you didn't save/version it before.
I would propose to:

• add a print in a terminal when this case happens
• stop the restore or at least save the current config.json to config_20210320_120034.json and then resume the restore
  Best regards,
  Victor

[johannesjo]

Thanks for opening this up. PRs are welcome, we also would need to consider the case, if this is run from the gnome shell widget though.