Bug 38287: Add missing rule_value access

Bug 38287: Add missing rule_value access

Test plan:
1) Access circuation rules:
http://localhost:8081/cgi-bin/koha/admin/smart-rules.pl
2) Scroll down to "Default checkout, hold and return policy". Enter nothing. Hit 'Save'.
3) Notice on page reload there is a Koha:: object on the bookings inputs
4) Save again -> ERROR
5) Apply patch. Repeat.

Signed-off-by: Sam Sowanick <sam.sowanick@corvallisoregon.gov>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>