pgsql: test_bitmapset: Improve handling of incorrect inputs

test_bitmapset: Improve handling of incorrect inputs

The SQL wrappers of the module relied on stringToNode(), that entirely
trusts its input. This commit applies an extra round of validation, to
prevent the test module from crashing on incorrect inputs, provided
through the SQL functions.

No backpatch, as this is no critical issue.

Author: Zsolt Parragi <zsolt(dot)parragi(at)percona(dot)com>
Reviewed-by: Greg Burd <greg(at)burd(dot)me>
Discussion: https://postgr.es/m/CAN4CZFOTQXMZvuPxweO4Fm7+sjrPJUqU-JvYKETLBxuhqgbPjw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/34c11958b6f12a90c0ec9fca3ce502a32280c30d

Modified Files
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.../test_bitmapset/expected/test_bitmapset.out | 24 ++++++++++++
.../modules/test_bitmapset/sql/test_bitmapset.sql | 10 +++++
src/test/modules/test_bitmapset/test_bitmapset.c | 44 ++++++++++++++++++++--
3 files changed, 75 insertions(+), 3 deletions(-)