Show OPAC-invisible copies in TPAC in staff context

We were not calling the staff variation of the copy count method; thus,
the record details template was skipping the copy table in the event
that all copies for a given record were marked as OPAC-invisible via
either copy visibility or shelving location visibility.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>