Bug 22593: Fix bad ternaries after bug 22008

Bug 22593: Fix bad ternaries after bug 22008

A series of ternaries were introduced when we moved to add_debit which
defaulted to 'user 0' should a userenv not be set.  This was incorrect
as userenv may well not be set (during cronscript runs for example) and
the new constraint would not allow such a default. We switch to 'undef'
here to satisfy the constraint.

Test plan
1) Ensure you have data in your system that would be caught by the
longoverdues cronjob.
2) Ensure you're sysprefs are setup to charge for lost items
3) Run the script and varify it runs to completion without errors

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>