Bug 25556: fix for unnecessary empty name/value pairs creation

Bug 25556: fix for unnecessary empty name/value pairs creation

During the web-install onboarding process, when the default circulation rule gets created, "circulation_rules" table gets populated with empty rule_name/rule_value items. This behavior differs from how the "unset" button on the smart-rules.pl page in "Default checkout, hold and return policy" group acts and leads to unpredictable bug when empty "holdallowed" rule_name prevents holds from any user.
This fix removes creation of these empty name/value pairs.

To reproduce:
    1) Start with an empty installation (or delete all circulation rules and press "unset" in hold and return policy section on /cgi-bin/koha/admin/smart-rules.pl page). This is to have the circulation_rules table empty so onboarding.pl will work.
    2) Go through the onboarding.pl process and create a default circulation rule.
    3) Make sure that circulation_rules table contains will contain empty "patron_maxonsiteissueqty", "max_holds", "patron_maxissueqty", "returnbranch", "holdallowed" and "hold_fulfillment_policy" fields.
    4) Apply the patch.
    5) Repeat steps 1 and 2.
    6) Observe that there are none of six mentioned above name/value pairs appeared.

To reproduce the bug with empty "holdallowed" rule_name:
    1) Repeat steps 1, 2 and 3 that are listed in the previous instruction of reproduction, in order to get empty "holdallowed" field.
    2) Find existing or create a new book with available status and place a holding on it.
    3) Observe the yellow notification window with "Cannot place hold. No items are available to be placed on hold." warning.
    4) Apply the patch.
    5) Repeat steps 1 and 2.
    6) Observe that hold was successfully placed and yellow notification does not appear anymore.

Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>