MDEV-5589 commit set up a policy to skip DROP TEMPORARY TABLE binary logging
in case the target table has not been "CREATEed" in binlog (no CREATE
Query-log-event was logged into the binary log).

It turns out that

1. the rule did not cover non-existing table DROPped with IF-EXISTS clause.
   The logged-create knowledge for the non-existing one does not even need
   MDEV-5589 patch, and

2. connection close disobeys it to trigger automatic DROP-IF-EXISTS
   binlogging.

Either 1 or 2 or even both is/are also responsible for unexpected binlog
records observed in MDEV-17863, actually rendering a referred
@@global.read_only irrelevant as far as the described stored procedure
definition *and* the ROW binlog-format are concerned.