Fix bug lp:782305

Analysis:
Both the wrong result and the valgrind warning were a result
of incomplete cleanup of the MIN/MAX subquery rewrite. At the
first execution of the query, the non-aggregate subquery is
transformed into an aggregate MIN/MAX subquery. During the
fix_fields phase of the MIN/MAX function, it sets the property
st_select_lex::with_sum_func to true.

The second execution of the query finds this flag to be ON.
When optimization reaches the same MIN/MAX subquery
transformation, it tests if the subquery is an aggregate or not.
Since select_lex->with_sum_func == true from the previous
execution, the transformation executes the second branch that
handles aggregate subqueries. This substitutes the subquery
Item into a Item_maxmin_subselect. At the same time elsewhere
it is assumed that the subquery Item is of type
Item_allany_subselect. Ultimately this results in casting the
actual object to the wrong class, and calling the wrong
any_value() method from empty_underlying_subquery().

Solution:
Cleanup the st_select_lex::with_sum_func property in the case
when the MIN/MAX transformation was performed for a non-aggregate
subquery, so that the transformation can be repeated.

sql/opt_subselect.cc

@@ -466,7 +466,7 @@ int check_and_do_in_subquery_rewrites(JOIN *join)
       /* Check if max/min optimization applicable */
       if (allany_subs)
         allany_subs->in_strategy|= (allany_subs->is_maxmin_applicable(join) ?
-                                    SUBS_MAXMIN :
+                                    (SUBS_MAXMIN_INJECTED | SUBS_MAXMIN_ENGINE) :
                                     SUBS_IN_TO_EXISTS);
 
       /*