Bug 16499: Remove "Use of uninitialized value" warnings in circulation.pl

Bug 16499: Remove "Use of uninitialized value" warnings in circulation.pl

If you search for a patron in the circulation module, you get:

Use of uninitialized value $barcode in string eq at
/home/koha/src/circ/circulation.pl line 84.
Use of uninitialized value $restoreduedatespec in string eq at
/home/koha/src/circ/circulation.pl line 170.

Test plan:
- Search for a patron and confirm the warnings are not displayed anymore
- Make sure this patch does not introduce regression on bug 14015

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 208637165ee40b2fe7d103c787a1f4f93b55d49b)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>