pgsql: Use [re]palloc_array() in buffile.c and fd.c

Use [re]palloc_array() in buffile.c and fd.c

The code paths patched in this commit fix some of remnants not addressed
by 1b105f9472bd. We should have more holes in the tree that could
benefit from stronger type safety guarantees. These hypothetical holes
could be addressed later; this finishes the job in storage/file/ for the
backend code.

Author: Tristan Partin <tristan(at)partin(dot)io>
Reviewed-by: Daniel Gustafsson <daniel(at)yesql(dot)se>
Reviewed-by: Sami Imseih <samimseih(at)gmail(dot)com>
Discussion: https://postgr.es/m/DKBAWPZ2QDOS.10Y3JDUNKFMXX@partin.io

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d64c805dea27d189904394ece7576762bece278c

Modified Files
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src/backend/storage/file/buffile.c | 6 ++----
src/backend/storage/file/fd.c | 4 ++--
2 files changed, 4 insertions(+), 6 deletions(-)