Avoid double-free() bug.
Avoid double-free() bug.

Spotted by Fortify static analysis tool.

treasure-data/prestogres-odbc,hlinnaka/psqlodbc,gavioto/psqlodbc,treasure-data/prestogres-odbc,gavioto/psqlodbc,treasure-data/prestogres-odbc,hlinnaka/psqlodbc,hlinnaka/psqlodbc,gavioto/psqlodbc