pgsql: Invalidate smgr_targblock in smgrrelease().

Invalidate smgr_targblock in smgrrelease().

In rare circumstances involving relfilenode reuse, it might have been
possible for smgr_targblock to finish up pointing past the end.

Oversight in b74e94dc.  Back-patch to 15.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://postgr.es/m/CA%2BhUKGJ8NTvqLHz6dqbQnt2c8XCki4r2QvXjBQcXpVwxTY_pvA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/81e36d3e0df8d3d7a3daa2e2216f96df23ffc96a

Modified Files
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src/backend/storage/smgr/smgr.c | 1 +
1 file changed, 1 insertion(+)