Bug 25690: SIP2: Don't allow checking out attached hold that is being transferred

Bug 25690: SIP2: Don't allow checking out attached hold that is being transferred

Items that are attached to a hold and being transferred (found = T) is
final decision and you cannot checkout those to other patrons.

To test (if you have applied all patches from bug 25690):
 1) prove t/db_dependent/SIP/Transaction.t => passes

To test (if you don't have all patches):
 1) Create hold and set pickup library to something else where the
    item is at
 2) Return the item and it should confirm the hold and start transfer
 3) Apply this patch
 4) Try to checkout this item now to some other patron via SIP2 and
    notice it doesn't allow it
 5) Revert this patch
 6) Notice you can now checkout somebody else's hold that is being transferred!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>