apply anyNA, and single definition of internal function

[mdsumner]

• converted any(is.na(x)) to anyNA(x) throughout
• moved check.na.nan out into a single definition
• put anyNA check before is.nan to short-circuit

Sadly, I can't see any speed up from this, feel free to review or discard,

(I'm not in any rush for the previous PR to be released btw. )

Cheers, Mike.

[davidcsterratt]

Sorry for the long delay looking at this PR and thank you for providing it. Now accepted.