pgsql: Suppress maybe-uninitialized warning.

Suppress maybe-uninitialized warning.

Following commit e035863c9a0, building with -O0 began triggering
warnings about potentially uninitialized 'workbuf' usage. While
theoretically the initialization isn't necessary since VARDATA()
doesn't access the contents of the pointed-to object, this commit
explicitly initializes the workbuf variable to suppress the warning.

Buildfarm members adder and flaviventris have shown the warning.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAD21AoCOZxfqnNgfM5yVKJZYnOq5m2Q96fBGy1fovEqQ9V4OZA@mail.gmail.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/b5c53b403c93393c3725558294cbf4dbfb575e42

Modified Files
--------------
src/backend/storage/large_object/inv_api.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)