Bug 37587: Fix priority of multiple item-level holds

Bug 37587: Fix priority of multiple item-level holds

The rank parameter is passed per biblio record, not per item. When
placing multiple item-level holds on one bib record, only $rank[0] is
defined.

To test:
1. System preference and circulation rule setup
    i. Set the system preference DisplayMultiItemHolds to Enable
    ii. Edit the default circulation rule to allow 5 holds per record
2. Find or create a bib with 4 or more items
3. Place several bib-level holds
4. Place 4 or more item-level holds at once on that same record
    i. Search for a patron to place the holds for (not one of the
       patrons you used in step 3)
    ii. Select "Hold a specific item"
    iii. Check the checkboxes for 4 or more items
    iv. Click Place hold
--> Note that one of the new item-level holds is at the end of the list
    as it should be, but the rest are out of order
5. Cancel the item-level holds from step 4
6. Apply patch and restart_all
7. Repeat step 4
--> All the new item-level holds are now at the end of the list

Signed-off-by: Roman Dolny <roman.dolny@jezuici.pl>
Signed-off-by: Paul Derscheid <paul.derscheid@lmscloud.de>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>