pgsql: Tighten proto_version parsing in pgoutput

Tighten proto_version parsing in pgoutput

This is similar to 58ff4a0a0867, but this time for the parameter
"proto_version", when given as a parameter to pgoutput for logical
replication. strtoul() lacked a check for an empty string, leading to
an inconsistent behavior depending on the platform.

The author has originally proposed a TAP test to check this empty value
pattern. I have added a cheaper SQL query, instead, test_decoding
including a test area where this is possible.

Author: Tristan Partin <tristan(at)partin(dot)io>
Discussion: https://postgr.es/m/DKBS2Z9CGARC.2T07O6TJYSE8B@partin.io

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/290bb8afe6b47adb8b080688bd97a710af351cb1

Modified Files
--------------
contrib/test_decoding/expected/replorigin.out | 4 ++++
contrib/test_decoding/sql/replorigin.sql | 3 +++
src/backend/replication/pgoutput/pgoutput.c | 5 +++--
3 files changed, 10 insertions(+), 2 deletions(-)