Prevent publishing "NaN" literally

[ndoo]

• Describe the scope of your change - Prevent publishing (return false) if passing a NaN float/double
• Describe any known limitations with your change. - You won't be able to see literal NaNs from MQTT feeds (but you should be tracing math/logic issues through your code/prototype, not through MQTT feeds and dashboards)
• Please run any tests or examples that can exercise your modified code. - WFM (compiles fine as a library to existing code)

[ndoo]

Ping, if there is no interest I shall close my PR.

[tyeth]

Hey 👋 thank you so much for your contribution!
I believe there was a decision last year to send NaN when appropriate for some sensors in the Adafruit WipperSnapper project. While I agree with your statement/assumption about keeping logic in the code, it's not always possible or desirable.

This PR is unlikely to be merged any time soon, but maybe in the future.

[ndoo]

Thanks, in that case I shall close the PR.