pgsql: Change bms_add_range to be a no-op for empty ranges

Change bms_add_range to be a no-op for empty ranges

In commit 84940644de93, bms_add_range was added with an API to fail with
an error if an empty range was specified. This seems arbitrary and
unhelpful, so turn that case into a no-op instead. Callers that require
further verification on the arguments or result can apply them by
themselves.

This fixes the bug that partition pruning throws an API error for a case
involving the default partition of a default partition, as in the
included test case.

Reported-by: Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>
Diagnosed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/16590.1532622503@sss.pgh.pa.us

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/192d1bbf99699de76473184c57fff9ff4b4246f4

Modified Files
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src/backend/nodes/bitmapset.c | 7 +++++--
src/test/regress/expected/partition_prune.out | 15 +++++++++++++++
src/test/regress/sql/partition_prune.sql | 7 +++++++
3 files changed, 27 insertions(+), 2 deletions(-)