pgsql: Revert unnecessary check for NULL

Revert unnecessary check for NULL

Jelte pointed out that this was unnecessary, but I failed to remove it
before pushing f6f0542266. Oops.

Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion:
https://www.postgresql.org/message-id/CAGECzQT%3DxNV-V%2BvFC7YQwYQMj0wGN61b3p%3DJ1_rL6M0vbjTtrA@mail.gmail.com
Backpatch-through: 18

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/5a26a3e4eeb279074421380ee332cc40690b2bac

Modified Files
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src/interfaces/libpq/fe-protocol3.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)