pgsql: Fix subscriber invalid memory access on DDL.

Fix subscriber invalid memory access on DDL.

This patch allows building the local relmap cache for a subscribed
relation after processing pending invalidation messages and potential
relcache updates.  Without this, the attributes in the local cache don't
tally with the updated relcache entry leading to invalid memory access.

Reported-by Jehan-Guillaume de Rorthais
Author: Jehan-Guillaume de Rorthais and Vignesh C
Reviewed-by: Amit Kapila
Backpatch-through: 10
Discussion: https://postgr.es/m/20191025175929.7e90dbf5@firost

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d6eca4958d78499b66aad9cf4b595b871c177e02

Modified Files
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src/backend/replication/logical/relation.c | 38 ++++++++++++++++++++----------
1 file changed, 25 insertions(+), 13 deletions(-)