Bug 27919: Return claims shouldn't change lost status if already set

Bug 27919: Return claims shouldn't change lost status if already set

This patch prevents a return claim from changing the lost status if it has already been set.

Test plan:
1) In system preferences, set the ClaimReturnedLostValue syspref to any value
2) Checkout an item to a patron
3) Set that item as lost, using a different status to the one you set in step 1
4) Create a return claim on the item
5) Check the item's lost status, it should now have been set to the value you set in step 1
6) Apply patch
7) reset_all
8) Repeat steps 1-5, this time the status should remain at the value you set in step 3 and not be overwritten by the return claim
9) Repeat steps 1,2,4 and 5 - this time the lost status should be set to the value you set in step 1 as we didn't have a pre-existing lost status

Signed-off-by: Andrew Fuerste Henry <andrewfh@dubcolib.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>