UPDATE VIEW USING OUTER SUBQUERY

Issue:
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While resolving a column which refers to a table/view in an
outer query, it's respecitve item object is marked with the
outer query's select_lex object. But when the column refers
to a view or if the column is part of a subquery in the
HAVING clause, an Item_ref object is created. While the
reference to the outer query is stored by the Item_ref
object, the same is not stored in it's real_item.

This creates a problem with the IN-TO-EXISTS optmization.
When there is an index over the column in the inner query,
it will be considered since the column's real_item object
will be mistaken for a local field. This will lead to a
crash.

SOLUTION:
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Under the current design, the only way to fix this issue is
to check the reginfo.join_tab for a NULL value. If yes, the
query should not be worrying about the key use.

The testcase and comments added as part of the fix for
Bug#17766653 have been backported.