Simple check for if the array property exists

Some customers have been reporting that they are seeing huge system.log files due to the extension:

Error appearing:
"2013-03-15T02:57:45+00:00 ERR (3): Notice: Undefined index: requester  in /home/zendesk/public_html/app/design/adminhtml/default/default/template/zendesk/dashboard/tabs/view.phtml on line 86"

/cc @chnorton