Doorbot 2 slow to react to fobs

[JackiePease]

Doorbot 2 is taking a long time to react to fobs being held against the reader

[johnmckerrell]

Tweaked the title and description to reflect the fact that it was doorbot2 having the issues.

I've solved them with this commit DoESLiverpool/logcards@69e64f2

This doorbot logs hot desk visits, if an attempt to do this fails (e.g. network down) it caches it and tries again later. For some reason a nil entry was being stored in the file, at this point the script would continually crash. I've fixed the nil handling and also tweaked a few other bits. Hopefully it'll be a bit more resilient now.

The doorbot is currently pointing at a log cards branch, after some short period of testing we should merge the branch to master and update the other doors.