pgsql: Suppress compiler warning about no function return value.

Suppress compiler warning about no function return value.

Compilers that don't know that ereport(ERROR) doesn't return
complained about the new coding in scanint8() introduced by
commit 101c7ee3e.  Tweak coding to avoid the warning.
Per buildfarm.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b31a9d7dd3bf8435fddf404c4b75236d0ea76d78

Modified Files
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src/backend/utils/adt/int8.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)