Bug 12632: Hold limits ignored for record level holds with item level itemtypes

Bug 12632: Hold limits ignored for record level holds with item level itemtypes

The crux of the issue is that if you are using item level itemtypes, but
are allowing biblio levels holds, those holds do not have items.

So, in CanItemBeReserved, when Koha counts the number of holds to
compare against the given rule, it will always give 0 ( except of course
for found holds, and the occasional item-level hold ).

So the query is saying "link each of these reserves to the reserved
item, and count the number of reserves this patron where the itemtype is
DVD". However, since these are all record level reserves, there are no
items to link to, and so when it looks for all reserves this and item
whose itemtype is DVD, it finds zero reserves!

This patch solves the problem by looking first at the item level
itemtype, and if it does not exist, then it looks at the record
level itemtype. For installations using record level itemtypes, the
behavior remains unchanged.

Test plan:
1) Enable item level itemtypes
2) Create two records with one item each of a given itemtype
3) Create a single issuing rule and limit the holds allowed for that
   itemtype to 1
4) Place a record level hold on your first record
5) Attempt to place a record level hold for the same patron on your
   second record. You should not be able to but you can!
6) Apply this patch
7) Repeat step 5, note you can no longer place the hold!

Signed-off-by: Paola Rossi <paola.rossi@cineca.it>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>