Check that numeric is zero

[Gabriel Furstenheim Milerud]

Hi,
I'm writing a Postgres native extension and I would like to check that a
numeric is zero.

My problem is that all exported methods like numeric_eq or numeric_sign
require me to have a numeric to start with, and const_zero is not exported
in numeric.c.

Any idea how to check it?

Thanks
Gabriel Fürstenheim