pgsql: Fix temporary tablespaces for shared filesets

Fix temporary tablespaces for shared filesets

A likely copy/paste error in 98e8b480532 from  back in 2004 would
cause temp tablespace to be reset to InvalidOid if temp_tablespaces
was set to the same value as the primary tablespace in the database.
This would cause shared filesets (such as for parallel hash joins)
to ignore them, putting the temporary files in the default tablespace
instead of the configured one. The bug is in the old code, but it
appears to have been exposed only once we had shared filesets.

Reviewed-By: Daniel Gustafsson
Discussion: https://postgr.es/m/CABUevExg5YEsOvqMxrjoNvb3ApVyH+9jggWGKwTDFyFCVWczGQ@mail.gmail.com
Backpatch-through: 9.5

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/4a1d21562a4f5d3cc5ccb5187c9fb44c26c38bc0

Modified Files
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src/backend/commands/tablespace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)