collect-mirror-stats errors when mirror is removed

[ja5087]

We are getting rootspam like:

Traceback (most recent call last):
  File "/usr/local/sbin/collect-mirrors-stats", line 195, in <module>
    sys.exit(main(args))
  File "/usr/local/sbin/collect-mirrors-stats", line 162, in main
    projects[log_filename.stem]['up'] += rx
KeyError: 'devuan'

I'm guessing (emphasis on guessing) this is due to me moving devuan -> devuan-cd and the old logs still containing devuan. Ideally this should not block stats collections.