librenms-health: If one device in a group does not have sensor data, the plugin returns UNKNOWN

[markuslf]

This issue respects the following points:

• [X] This is a bug, not a question or a setup/configuration issue.
• [X] This issue is not already reported on Github (I've searched it).
• [X] I use the latest release of the Monitoring Plugins (https://github.com/Linuxfabrik/monitoring-plugins/releases).
• [X] I agree to follow Monitoring Plugins's Code of Conduct.

Bug description

Including a 404 Not Found.

Steps to reproduce - Plugin call

Later, we get "Everything is ok (although no health data returned)."

Steps to reproduce - Plugin Version

n/a

Steps to reproduce - Data

No response

Python version

No response

Environment

n/a

Application

No response

Python modules

No response

Additional info

No response