pgsql: Fix the initial sync tables with no columns.

Fix the initial sync tables with no columns.

The copy command formed for initial sync was using parenthesis for tables
with no columns leading to syntax error. This patch avoids adding
parenthesis for such tables.

Reported-by: Justin G
Author: Vignesh C
Reviewed-by: Peter Smith, Amit Kapila
Backpatch-through: 15
Discussion: http://postgr.es/m/18203-df37fe354b626670@postgresql.org

Branch
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REL_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/1b6da28e0668eb977dcab6987d192ddedf32b752

Modified Files
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src/backend/replication/logical/tablesync.c | 28 ++++++++++++++++++----------
src/test/subscription/t/001_rep_changes.pl  | 17 ++++++++++++++++-
2 files changed, 34 insertions(+), 11 deletions(-)