pgsql: Relocate a badly placed Assert in COPY FROM code

Relocate a badly placed Assert in COPY FROM code

There's not much point in asserting a pointer isn't NULL after some code
has already dereferenced that pointer.

Adjust the code so that the Assert occurs before the pointer dereference.

The Assert probably has questionable value in the first place, but it
seems worth keeping around to document the contract between
CopyMultiInsertInfoNextFreeSlot() and its callers.

Author: Amul Sul <sulamul(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAAJ_b94hXQzXaJxTLShkxQUgezf_SUxhzX9TH2f-g6gP7bne7g@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/bd8fe12ef3f727ed3658daf9b26beaf2b891e9bc

Modified Files
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src/backend/commands/copyfrom.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)