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)