Retargeting a cancelled hold can cause problems with uncancelled captured holds

When viewing a patron's cancelled holds, it is possible to select a hold and choose "Find Another Target" from the actions menu.

Since cancelled holds retain the value in the current_copy field, it's possible for another captured hold also to reference the same copy.

Retargeting the cancelled hold will change the status of the currently captured item.

Steps to reproduce:

-Place two holds on a record for different patrons, Patron A and Patron B.

-Check in the item to capture the hold for Patron A. Item is On holds shelf.

-Cancel the hold for the captured item.

-Check in the item to capture the hold for Patron B. Item in On holds shelf.

-Retrieve Patron A and view the patron's cancelled holds.

-Select the hold and choose Find another target from the Actions menu.

-The item's status will now be Reshelving.

-Patron A's hold will show Hold Status -1

A straighforward fix would be to not allow cancelled holds to be retargeted.