when there are nested subqueries, and a field in a subquery is
resolved as an outer reference to a table few levels up, all subqueries
the subquery with a reference and all subqueries up to subquery with
the table must be marked as dependent.

in the text protocol and PS-prepare step it happens in
Item_field::fix_outer_field in a loop that walks contexts
using context->outer_context.

in PS-execute step Item_field->cached_table is set and subqueries
are walked in a PS-only mark_select_range_as_dependent(),
which inconsistently walks SELECT_LEX'es using select_lex->outer_select().

Fix mark_select_range_as_dependent() to walk contexts, not SELECT_LEX'es,
to have the same logic both in prepare and execute steps.

This fixes a crash in main.insert_returning in --ps-protocol