pgsql: Build subscription conninfo after checking that it's enabled.

Build subscription conninfo after checking that it's enabled.

If a subscription is disabled, don't try to build conninfo because
that may generate a confusing error and try to disable an
already-disabled subscription.

Partially addresses finding 5 in report from linked discussion.

Reported-by: Noah Misch <noah(at)leadboat(dot)com>
Reviewed-by: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Discussion: https://postgr.es/m/20260710195902.4f.noahmisch%40microsoft.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/8b73ceb78f8e40f82ef965b9a1e15a8344c61daf

Modified Files
--------------
src/backend/replication/logical/worker.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)