When flattening a view that is the right operand of a LEFT JOIN, using

When flattening a view that is the right operand of a LEFT JOIN, using
the optimization of check-in [41c27bc0ff1d3135], always insert the
TK_IF_NULL_ROW expression nodes, even for TK_COLUMN expressions, as
the TK_COLUMN might be a column from an outer query and hence still need
to be NULLed out. This fixes the problem described by
[forum:/forumpost/26387ea7ef|forum post 26387ea7ef].

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