Add ability to call ut_set_error_message_handler with ut_ignore without argument

[darianboggs]

I am using udunits-2.2.28 as a library for a Fortran application, and I need to set the error message handler to ut_ignore from Fortran.

I have written Fortran interfaces to the udunits library procedures I need to use, but I cannot write an interface to ut_ignore because of the variadic list.

Since I want to disable the error handler, I need a 0 argument function to call ut_set_error_message_handler with ut_ignore or some way to call ut_set_error_meassage_handler without passing ut_ignore.