The absence of holds-triggered recall rules should not break hold targeting

The absence of holds-triggered recall rules should not break hold targeting

Thanks to Galen Charlton for pointing out that if rules were not set for
holds-triggered recalls, then all hold targeting would break because of
an assumption the code made that one could invoke the ->{value} member
of the OU settings. But of course the return value for an unset OU setting
is undef, not an object with an undef ->{value} member.

This should unbreak that code path.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@18816 dcc99617-32d9-48b4-a31d-7c20da2025e4