[Bug] KeyError in logs

[alexiri]

Describe the bug Checking the logs, I found the following output:

2022-05-30 13:58:21,867 - octoprint.plugins.detailedprogress - INFO - Printing stopped. Detailed progress stopped.
2022-05-30 13:58:21,895 - octoprint.plugins.stats - INFO - Printer Stats - on_event
2022-05-30 13:58:21,895 - octoprint.plugin - ERROR - Error while calling plugin stats
Traceback (most recent call last):
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint/plugin/__init__.py", line 273, in call_plugin
    result = getattr(plugin, method)(*args, **kwargs)
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint/util/__init__.py", line 1688, in wrapper
    return f(*args, **kwargs)
  File "/home/pi/oprint/lib/python3.7/site-packages/octoprint_stats/__init__.py", line 939, in on_event
    user = payload["user"]
KeyError: 'user'

Environment information:

• Octoprint Version: [eg. 1.4.0] 1.8.1
• Browser: [e.g. chrome, safari]
• Python Version: [eg. Python 3.8] Python 3.7.3
• Operating system that Octoprint is running on: [eg. Debian 10.5, Windows 10] OctoPi