Viewing client results in `Notice: Undefined variable: rows in hosting_client_view()`

Attempting to view which sites are owned by a particular client results in the following error message appearing, and no list of sites for the client showing up:

Notice: Undefined variable: rows in hosting_client_view() (line 645 of /var/aegir/hostmaster-7.x-3.4/profiles/hostmaster/modules/aegir/hosting/client/hosting_client.module).