ovsdb-tool: Fix datum leak in the show-log command.

Fixes: 4e92542 ("ovsdb-tool: Make "show-log" convert raw JSON to easier-to-read syntax.")
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Acked-by: Dumitru Ceara <dceara@redhat.com>

ovsdb/ovsdb-tool.c

@@ -471,6 +471,7 @@ print_db_changes(struct shash *tables, struct shash *names,
                                 ds_init(&s);
                                 ovsdb_datum_to_string(&datum, type, &s);
                                 value_string = ds_steal_cstr(&s);
+                                ovsdb_datum_destroy(&datum, type);
                             } else {
                                 ovsdb_error_destroy(error);
                             }