Bug 37055: Check count of holds, not if defined

Bug 37055: Check count of holds, not if defined

To test:
 - enable WaitingNotifyAtCheckout
 - have or create a waiting hold for a patron
 - check out an item to a different patron who does not have a waiting hold
 - Koha says "This patron has waiting holds that are available for checkout"
 - Apply patch
 - Reload patron (click 'Checkout' tab)
 - Check out an item - no warning
 - Find the patron with waiting hold
 - Check out an item - warning
 - Checkout the waiting item - no warning

Signed-off-by: Brendan Lawlor <blawlor@clamsnet.org>
Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>