Return EAI_AGAIN for AF_UNSPEC when herrno is TRY_AGAIN (BZ #16849)

getaddrinfo correctly returns EAI_AGAIN for AF_INET and AF_INET6
queries.  For AF_UNSPEC however, an older change
(a682a1bf553b1efe4dbb03207fece5b719cec482) broke the check and due to
that the returned error was EAI_NONAME.

This patch fixes the check so that a non-authoritative not-found is
returned as EAI_AGAIN to the user instead of EAI_NONAME.