pgsql: Fixup various older misuses of appendPQExpBuffer

Fixup various older misuses of appendPQExpBuffer

Use appendPQExpBufferStr when there are no parameters and
appendPQExpBufferChar when the string length is 1.

Unlike 3fae25cbb, which fixed this issue for code that was new to v18,
this one fixes up instances which exist in the backbranches. We've
historically tried to maintain this standard and if we're going to
continue doing that, then we won't be doing that selectively based on
when the code was introduced. Now seems like a good time to flush out the
existing misuses. Waiting until v19 just prolongs their existence in
terms of released versions that the misuses exist in.

Author: David Rowley <drowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAApHDvoARMvPeXTTC0HnpARBHn-WgVstc8XFCyMGOzvgu_1HvQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1bd08f6ba56ac9b23dc46ab634d82327395e882e

Modified Files
--------------
src/bin/initdb/initdb.c | 4 ++--
src/bin/pg_basebackup/pg_createsubscriber.c | 24 ++++++++++++------------
src/bin/pg_dump/pg_dump.c | 24 ++++++++++++------------
src/bin/pg_dump/pg_dumpall.c | 2 +-
src/bin/pg_upgrade/pg_upgrade.c | 8 ++++----
src/bin/psql/common.c | 2 +-
src/bin/scripts/vacuumdb.c | 16 ++++++++--------
7 files changed, 40 insertions(+), 40 deletions(-)