Fixing memory leak in pg_upgrade

According to Coverity, there's a memory leak bug in transfer_all_new_dbs().
    mappings = gen_db_file_maps(old_db, new_db, &n_maps, old_pgdata,                                new_pgdata);
    if (n_maps)    {        print_maps(mappings, n_maps, new_db->db_name);

#ifdef PAGE_CONVERSION        pageConverter = setupPageConverter();
#endif        transfer_single_new_db(pageConverter, mappings, n_maps,                               old_tablespace);
        pg_free(mappings);    }
-----> leaks "mappings"}return;
}

This is because gen_db_file_maps() allocates memory even if n_maps == 0.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
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