[css-typed-om] CSSNumericValue.div() and invert don't specify handling of divide-by-zero

[dbaron]

The definition of CSSNumericValue.div() and the definition of the invert concept immediately following (which it depends on) don't specify the handling of division by zero. However, it seems like they need to, given that the second step of invert is:

If this is a CSSUnitValue object with unit internal slot set to "number", return a new CSSUnitValue with the unit internal slot set to "number", and a value internal slot set to the inverse of this’s.

which could certainly do division by zero, and is required to place the result in a double (not unrestricted double).

[dbaron]

Looks good, thanks.