Fix incorrect pg_stat_io output on 32-bit machines.
pg_stat_get_io() applied TimestampTzGetDatum twice to the
stat_reset_timestamp value. On 64-bit builds that's harmless because
TimestampTzGetDatum is a no-op, but on 32-bit builds it results in
displaying garbage in the stats_reset column of the pg_stat_io view.
Bug dates to commit
a9c70b46d which introduced pg_stat_io, so
back-patch to v16 where that came in.
Bertrand Drouvot
Discussion: https://postgr.es/m/Ztrd+XcPTz1zorkg@ip-10-97-1-34.eu-west-3.compute.internal