Return NaN and warn instead of throwing if measure fails

[naftalibeder]

Right now, calling measure on a ref whose view does not exist throws an error, which needs to be caught by the caller.

Would there be any interest in tweaking it to send a console.warn and return { x: NaN, ... } instead? In my experience so far, it feels a bit over-sensitive.

[naftalibeder]

I opened a PR here: #3453