pgsql: Avoid memcpy() with same source and destination in pgstat_recv_r

Avoid memcpy() with same source and destination in pgstat_recv_replslot.

Same type of issue as in commit 53d4f5fef and earlier fixes; also
found by apparently-more-picky-than-the-buildfarm valgrind testing.
This one is an oversight in commit 986816750.  Since that's new in
HEAD, no need for a back-patch.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ed6329cfa975a13c58c44676464585cda5d317b3

Modified Files
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src/backend/postmaster/pgstat.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)