Bug 27069: (follow-up) Only display rules if one is set

Bug 27069: (follow-up) Only display rules if one is set

Testing that the rule is != 'hold_allowed' is true for each itemtype where
the rule is not set. This means it appears that no holds are allowed
for any item type if no rules are set

To test:
1 - With a fresh testing DB or no holdallowed rule set, you can use SQl below to clear:
    DELETE from circuation_rules WHERE rule_name='holdallowed';
2 - Load smart-rules.pl (Administration->Circulation and fines rules)
3 - Scroll to "Default holds policy by item type"
4 - Note all item types appear as 'No holds allowed'
5 - Apply patch
6 - Reload
7 - All clear
8 - Confirm adding rules displays correctly

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>