Bug 35310: Only show 'Current renewals' <li> entry if there are current renewals

Bug 35310: Only show 'Current renewals' <li> entry if there are current renewals

'Current renewals' is always showing, even if empty.

Test plan:
1) Checkout an item to Koha user, barcode 39999000003192
2) Renew that barcode
3) Visit the items page of the biblio record, click on "View" in front of "Current renewals"
/cgi-bin/koha/catalogue/moredetail.pl?biblionumber=76
4) Notice all items have the 'Current renewals' label entry, but only the checked out item in step 1) has the 'Current renewals' label entry
5) Apply patch. Notice only the item with current renewals is showing the 'Current renewals' label entry with the respective value.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>