The duplicate slot maybe produce by planner when select constant stmt

[EmmyMiao87]

Describe the bug
The duplicate slot maybe produce by planner when select constant stmt

select 1 from test where k1=1
A slot will be added in tuple when tuple's materialized slots is empty.

select 1, k1 from test where k1=1

But k1 is duplicated with the column k1 in where clause.
This will cause the predicate to be incorrectly pushed down to the storage engine when the query is executed.