Bug 35432: Add _can_item_fill_request subroutine

Bug 35432: Add _can_item_fill_request subroutine

There are a series of repeated checks throughout MapItemsToHoldRequests.

This patch simply consolidates them into a single routine that can be called.

To test:
1 - prove t/db_dependent/HoldsQueue.t
2 - Confirm it passes before and after this patch is applied

Signed-off-by: Phil Ringnalda <phil@chetcolibrary.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>