pgsql: Tweak the existing special case for AIX in pg_getaddrinfo_all()

Log Message:
-----------
Tweak the existing special case for AIX in pg_getaddrinfo_all() to handle
yet another failure case in AIX's getaddrinfo(). Per report and patch
by Andrew Chernow.

Modified Files:
--------------
pgsql/src/backend/libpq:
ip.c (r1.43 -> r1.44)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/libpq/ip.c?r1=1.43&r2=1.44)