ovsdb-idl: Fix memory leak

ovsdb-idl: Fix memory leak

In testcase "simple idl, conditional, multiple clauses in condition - C",
valgrind reports a memory leak with the following call stack.
    xmalloc (util.c:112)
    resize (hmap.c:100)
    ovsdb_idl_condition_clone (ovsdb-idl.c:1075)
    ovsdb_idl_set_condition (ovsdb-idl.c:1095)
    update_conditions (test-ovsdb.c:2299)
    do_idl (test-ovsdb.c:2388)
    ovs_cmdl_run_command__ (command-line.c:115)
    main (test-ovsdb.c:73)

Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>