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 <[email protected]>
Discussion: https://postgr.es/m/CAD21AoCOZxfqnNgfM5yVKJZYnOq5m2Q96fBGy1fovEqQ9V4OZA@mail.gmail.com
        char        data[LOBLKSIZE + VARHDRSZ];
        /* ensure union is aligned well enough: */
        int32       align_it;
-   }           workbuf;
+   }           workbuf = {0};
    char       *workb = VARDATA(&workbuf.hdr);
    HeapTuple   newtup;
    Datum       values[Natts_pg_largeobject];
        char        data[LOBLKSIZE + VARHDRSZ];
        /* ensure union is aligned well enough: */
        int32       align_it;
-   }           workbuf;
+   }           workbuf = {0};
    char       *workb = VARDATA(&workbuf.hdr);
    HeapTuple   newtup;
    Datum       values[Natts_pg_largeobject];