Failsafe path when phpBB2 config table has missing rows

In theory this should never occur with a clean install of phpBB2, though the db I'm testing this was was converted from phpBB1.x and appears to have had the values smtp_username and smtp_password missing since forever.

The converter dies with:

[phpBB Debug] PHP Notice: in file /includes/functions_convert.php on line 1255: Undefined index: smtp_username

[phpBB Debug] PHP Notice: in file /includes/functions_convert.php on line 1255: Undefined index: smtp_password

Since phpBB3 needs to be installed in the first place before the converter can be run, perhaps it'd be possible to fall-back to the value used on the phpBB3 install?