pgsql: Initialize unused ExprEvalStep fields.

Initialize unused ExprEvalStep fields.

ExecPushExprSlots didn't initialize ExprEvalStep's resvalue/resnull
steps as it didn't use them. That caused wrong valgrind warnings for
an upcoming patch, so zero-intialize.

Also zero-initialize all scratch ExprEvalStep's allocated on the
stack, to avoid issues with similar future omissions of non-critial
data.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fc96c6942551dafa6cb2a6000cbc9b20643e5db3

Modified Files
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src/backend/executor/execExpr.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)