pgsql: Supress convertion of zero hours to '12' for intervals when using

Log Message:
-----------
Supress convertion of zero hours to '12' for intervals when using
to_char with HH, e.g.

    to_char(interval '0d 0h 12m 44s', 'DD HH24 MI SS');

now returns:

     00 00 12 44

not:

     00 12 12 44

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        formatting.c (r1.163 -> r1.164)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/formatting.c?r1=1.163&r2=1.164)