Coming from bitcoin#11017

This PR intends to plug some leaks. It specifically implements adherence to the requirement in BDB to close a handle which failed to open (https://docs.oracle.com/cd/E17276_01/html/api_reference/C/dbopen.html):

The DB->open() method returns a non-zero error value on failure and 0 on success. If DB->open() fails, the DB->close() method
must be called to discard the DB handle.