Problem:
In query like
select 1 from .. order by match .. against ...;
causes a debug assert failue.

Analysis:
In union type query like

(select * from order by a) order by b;
or
(select * from order by a) union (select * from order by b);

We skip resolving of order by a for 1st query and order by of a and b in 
2nd query.


This means that, in case when our order by have Item_func_match class, 
we skip resolving it.
But we maintain a ft_func_list and at the time of optimization, when we 
Perform FULLTEXT search before all regular searches on the bases of the 
list we call Item_func_match::init_search() which will cause debug assert 
as the item is not resolved.


Solution:
We will skip execution if the item is not fixed and we will not 
fix index(Item_func_match::fix_index()) for which 
Item_func_match::fix_field() is not called so that on later changes 
we can check the dependency on fix field.