internal/number: convert non-numbers to NaN

Change-Id: I378d586b72bd577aabee482372199902666dbccb
Reviewed-on: https://go-review.googlesource.com/58911
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2 files changed