Fix memory leak when inserting tuple at relation creation for CTAS
The leak has been introduced by
763f2ed which has addressed the problem
for transient tables, and forgot CREATE TABLE AS which shares a similar
logic when receiving a new tuple to store into the newly-created
relation.
Author: Jeff Janes
Discussion: https://postgr.es/m/CAMkU=1xZXtz3mziPEPD2Fubbas4G2RWkZm5HHABtfKVcbu1=Sg@mail.gmail.com