pgsql: Fix memory leak in printtup.c.

Fix memory leak in printtup.c.

Commit f2dec34e1 changed things so that printtup's output stringinfo
buffer was allocated outside the per-row temporary context, not inside
it.  This creates a need to free that buffer explicitly when the temp
context is freed, but that was overlooked.  In most cases, this is all
happening inside a portal or executor context that will go away shortly
anyhow, but that's not always true.  Notably, the stringinfo ends up
getting leaked when JDBC uses row-at-a-time fetches.  For a query
that returns wide rows, that adds up after awhile.

Per bug #15700 from Matthias Otterbach.  Back-patch to v11 where the
faulty code was added.

Discussion: https://postgr.es/m/15700-8c408321a87d56bb@postgresql.org

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/adf27de8eabbf43b049d1a1bb72780e53e8ea863

Modified Files
--------------
src/backend/access/common/printtup.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)