Bug 24446: (follow-up) Handle cases of pre-existing transfers

Bug 24446: (follow-up) Handle cases of pre-existing transfers

This is a long standing bug in stockrotation (and transfers in general)
where by if a transfer is in progress and another transfer is requested
then the original transfer is inexplicitly cancelled. This patch updates
the stockrotation code to handle queued transfers, either adding a
StockrotationAdvance transfer to the queue when an in progress transfer
was triggered to fulfil a Reserve, or otherwise cancelling the transfer
as stockrotation should take precidence.

To test
1/ Run t/db_dependent/StockRotationsItems.t.
2/ Signoff

Signed-off-by: Kathleen Milne <kathleen.milne@cne-siar.gov.uk>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>