pgsql: Make ExecForPortionOfLeftovers() obey SRF protocol.

Make ExecForPortionOfLeftovers() obey SRF protocol.

Before each call to the SRF, initialize isnull and isDone, as per the
comments for struct ReturnSetInfo. This fixes a Coverity warning
about rsi.isDone not being initialized. The built-in
{multi,}range_minus_multi functions don't return without setting it,
but a user-supplied function might not be as accommodating.

We also add statistics tracking around the function call, which
will be expected once user-defined withoutPortionProcs functions
are supported, and a cross-check on rsi.returnMode just for
paranoia's sake.

Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Co-authored-by: Paul A Jungwirth <pj(at)illuminatedcomputing(dot)com>
Discussion: https://postgr.es/m/4126231.1776622202@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/207cb2abcba00f78d57cdaca896f41c9453b0f2f

Modified Files
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src/backend/executor/nodeModifyTable.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)