Bug 12362: (QA follow-up) Fix ModItemTransfer cancellation handling

Bug 12362: (QA follow-up) Fix ModItemTransfer cancellation handling

ModItemTransfer is still used, sparingly. It force cancels transfers
regardles of whether they are already marked as in_transit. We do not,
however, want to enqueue a return transfer in this case as
ModItemTransfer is itself an enqueue function.  This patch updates the
internal logic of ModItemTransfer to enqueue the passed transfer prior
to cancelling the pre-existing one.. in this way the result is one
cancelled transfer and one new transfer and not three transfers.

Test plan
1/ Run t/db_dependant/Items.t and verify it fails prior to applying this
patch
2/ Apply patch and run the test again, verifying it now passes.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>