Add isFinite check on Duration.fromDurationLike(<numeric>)

[dobon]

Bug fix for #1118

This patch addresses a bug where Interval.after(new Date(0), Infinity) fails to throw an error, and the Infinity is interpreted as 0.

I'd say the bug here is that we're returning a "valid" Interval object. Somewhere in there the infinity is being treated as effectively a zero. --icambron, in the issue thread

The underlying problem is that Interval.after and Interval.before create a Duration from their second argument using the Duration.fromDurationLike method, and the fromDurationLike method has different behavior based on whether its argument is numeric, a luxon Duration, or an object. The bug is that we were checking isNumber, but not checking isFinite, which allows invalid numerics (ie: Infinity and NaN).

So in this patch I've added the necessary isFinite check and unit tests for fromDurationLike(Infinity) and fromDurationLike(NaN).

[diesieben07]

I think a better place to fix this would be asNumber, which is where we're already checking for NaN. That has the effect of also disallowing infinities in other places, such as DateTime.fromObject.

[diesieben07]

Thank you!