Avoid crashing when passing a Number and a format to Moment constructor.

Passing a Number value and a format to the Moment constructor causes Moment to throw a JS error (from within `makeDateFromStringAndFormat`). Seems like Moment isn't designed to handle this (preferring instead `moment.utc()` but it should probably not throw errors in this case when it can parse the Number and ignore the format.
This doesn't just take strings. You can see just below there's code there to handle the array case, which your added condition is preventing.