pgsql: Silence compiler warnings from some older compilers.

Silence compiler warnings from some older compilers.

Since a117cebd6, some older gcc versions issue "variable may be used
uninitialized in this function" complaints for brin_summarize_range.
Silence that using the same coding pattern as in bt_index_check_internal;
arguably, a117cebd6 had too narrow a view of which compilers might give
trouble.

Nathan Bossart and Tom Lane. Back-patch as the previous commit was.

Discussion: https://postgr.es/m/20220601163537.GA2331988@nathanxps13

Branch
------
REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/37290f7f5a9acf9c88c5d65490b7ec24776ba332

Modified Files
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contrib/amcheck/verify_nbtree.c | 2 +-
src/backend/access/brin/brin.c | 6 ++++++
2 files changed, 7 insertions(+), 1 deletion(-)