pgsql: Silence assorted "variable may be used uninitialized" warnings.

Silence assorted "variable may be used uninitialized" warnings.

All of these are false positives, but in each case a fair amount of
analysis is needed to see that, and it's not too surprising that not all
compilers are smart enough.  (In particular, in the logtape.c case, a
compiler lacking the knowledge provided by the Assert would almost surely
complain, so that this warning will be seen in any non-assert build.)

Some of these are of long standing while others are pretty recent,
but it only seems worth fixing them in HEAD.

Jaime Casanova, tweaked a bit by me

Discussion: https://postgr.es/m/CAJGNTeMcYAMJdPAom52dppLMtF-UnEZi0dooj==75OEv1EoBZA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9a725f7b5cb7e8c8894ef121b49eff9c265245c8

Modified Files
--------------
src/backend/access/transam/xloginsert.c | 2 +-
src/backend/catalog/objectaddress.c     | 2 ++
src/backend/utils/sort/logtape.c        | 2 +-
src/bin/pgbench/pgbench.c               | 7 ++++---
4 files changed, 8 insertions(+), 5 deletions(-)