Bug 14930 - Leaving OpacFineNoRenewals blank blocks renewals, but should disable...

Bug 14930 - Leaving OpacFineNoRenewals blank blocks renewals, but should disable feature

To Test
- Borrower has some fines and checkouts
- Leave OPACFineNoRenewals empty/blank
- Try to renew items in the OPAC
- notice error message
- Add a big value to OpacFineNoRenewals
- notice renewals work

Leaving the OPACFineNoRenewals empty will disable the feature.

Patch works as expected.(Amended to format the commit message and to
remove a warn on line 112 / MV)
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com