Bug #41057: mysql_update fails FATAL ERROR: Failed to create temporary file for defaults
Bug #41057: mysql_update fails FATAL ERROR: Failed to create temporary file for defaults

mysql_upgrade was passing an non-initialized non-null tmpdir to create_temp_file() if no 
--tmpdir was specified. This prevents create_temp_file() from taking the system 
temporary file path and as a result mysql_upgrade was trying to open a file in a 
directory that it may not have write access to.
Fixed by making sure mysql_upgrade will pass a zero length temp dir string to 
create_temp_file() if no --tmpdir is specified.

ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,ollie314/server,ollie314/server,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,flynn1973/mariadb-aix,natsys/mariadb_10.2,davidl-zend/zenddbi,natsys/mariadb_10.2,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,ollie314/server,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,davidl-zend/zenddbi,slanterns/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,davidl-zend/zenddbi,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,flynn1973/mariadb-aix,flynn1973/mariadb-aix