Better handling of bp_group_document file download attempts when file is not present
See #14304. Clicking a bp_group_document item title in the Group Library triggers our download mechanism. See
cac_catch_group_doc_request()in plugins/cac-bp-custom-includes/group-documents.php. If the source file is not found in its expected location, we should serve an error or do something more useful than redirecting to the homepage. It looks like we attempt to send users to the group library, but it appears not to be working for some reason.
This is relatively low priority because the case should never arise in the normal course of events.