LP#1753005: Avoid copy alert error for call numbers with no copies

LP#1753005: Avoid copy alert error for call numbers with no copies

When displaying the Holdings View tab for a bib in the web staff client,
if a volume record has no copies, a Javascript error gets thrown.

Item-less volumes still end up in svc.copies at this point, so at the
moment it is necessary to check whether copy_alerts actually exists.
Some renaming might also be in order to clarify that svc.copies doesn't
necessarily contain /only/ fleshed acp records.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Dan Wells <dbw2@calvin.edu>