When during the optimization an item is moved to the upper select
the item's context left unchanged. This caused wrong result in the 
PS/SP mode.
The Item_ident::remove_dependence_processor now sets the context
of the select to which the item is moved to.

mysql-test/r/subselect.result:
  The test case for the bug#46051 is adjusted.
mysql-test/t/subselect.test:
  The test case for the bug#46051 is adjusted.
sql/item.cc:
  Bug#46051: Incorrectly market field caused wrong result.
  The Item_ident::remove_dependence_processor now sets the context
  of the select to which the item is moved to.