Allocating more space than required for JOIN_TAB array for a query with SJM table

An example

EXPLAIN SELECT * FROM one_k

WHERE  a IN (SELECT t10.b 

                           FROM t10, t11, t12, t13, t14

                           WHERE t11.a=t10.b+1 AND t12.a=t10.b AND

                                           t13.a=t10.b AND t14.a=t10.b);

this case uses Semi Join Materializaion and the subquery is added to the table list of select #1.
The total number of tables for select #1 is 1(one_k)+ 5(inner_tables) + 1(SJM_TABLE). But for the top level we are only considered about 2 and should only have two JOIN_TAB structures.

In the function JOIN::get_best_combination
we allocate space for JOIN_TAB array like

  if (!(join_tab= (JOIN_TAB*) thd->alloc(sizeof(JOIN_TAB)*

                                        (top_join_tab_count + aggr_tables))))

In the debugger
(gdb) p top_join_tab_count
$8 = 6

So in this issue we would like to correct the value of top_join_tab_count, to only consider the tables that would be present at the top level. In this case
the value of top_join_tab_count should be 2.