LP 1827250: Fix Last Captured Hold Check for Holds Shelf

LP 1827250: Fix Last Captured Hold Check for Holds Shelf

When the current copy on an on shelf hold is the same as that on some
uncaptured holds, the hold fails to appear on the hold shelf when it
should.  This comes down to some SQL in the storage function to
retrieve wide holds: open-ils.storage.action.live_holds.wide_hash.

The intent of the new code is to check that the current hold matches
the most recently captured hold for the copy.  However, the order by
in the query fails to take into account holds with a NULL capture time
on the same copy will sort before the captured holds.  This patch
rectifies this situation by adding "NULLS LAST" to the order by.

Signed-off-by: Jason Stephenson <jason@sigio.com>