pgsql: Make BufFileWrite() void.

Make BufFileWrite() void.

It now either returns after it wrote all the data you gave it, or raises
an error.  Not done in back-branches, because it might cause problems
for external code.

Discussion: https://postgr.es/m/CA%2BhUKGJE04G%3D8TLK0DLypT_27D9dR8F1RQgNp0jK6qR0tZGWOw%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f5d18862bbb327b67cd0f33f3d11351096080665

Modified Files
--------------
src/backend/storage/file/buffile.c | 4 +---
src/include/storage/buffile.h      | 2 +-
2 files changed, 2 insertions(+), 4 deletions(-)