Partially fix #72506: idn_to_ascii for UTS #46 incorrect for long domain names

Partially fix #72506: idn_to_ascii for UTS #46 incorrect for long domain names

We don't actually fix this issue wrt. the empty $info array, because it is
not clear what this array should contain and we're concerned about the
potential BC break, but at least we fix the inconsistent handling of
resulting domains with 255 bytes (which raise an error), and longer domains
(which just return FALSE), what has to be considered a very minor BC break
if at all.