group by push down: HAVING optimized out causes crash

Using an engine that defines the new group by push down API;
When running this query:

CREATE TABLE t1 (a int) engine=columnstore;

INSERT INTO t1 VALUES (1), (2), (1), (3), (2), (1);

SELECT a FROM t1 GROUP BY a HAVING 1 != 1;

mysqld crashes at sql_select.cc:2431 bzero(curr_tab, sizeof(JOIN_TAB));

At this point curr_tab is NULL.

I don't know if it should be NULL (probably should), but we shouldn't be bzero-ing a NULL pointer.