pgsql: postgres_fdw: Fix possible crash after option initialization fai

postgres_fdw: Fix possible crash after option initialization fails

An out-of-memory error while initializing postgres_fdw's option array
could cause a later operation using postgres_fdw in the same session
to crash.

InitPgFdwOptions() assigned postgres_fdw_options before filling the
array. If MemoryContextStrdup() failed while copying an option name,
the pointer remained non-NULL, causing subsequent calls to skip
initialization and use the incomplete array.

Fix this by building the array using a local pointer and assign
postgres_fdw_options only after initialization is complete, so that
a failed attempt can be retried safely.

Backpatch to v19, where commit 0f9d4d7c12d introduced the
MemoryContextStrdup() calls that made this failure possible.

Author: Lucas Jeffrey <luquijeffrey(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAObkL7OzJWqNg170qM=+zQjw1-EyvKc8LjWizjcnw4fEjB5mnw@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/1d4324a2a302514a24908435dede693cff81fa37

Modified Files
--------------
contrib/postgres_fdw/option.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)