views: prevent backtrace when no server is available

Define the timestamp in the codepath executed when no server is
found active. Prevent the web to show a backtrace because the
timestamp variable is used but not defined as it is only created
when a server is found.

ogcp/views.py

@@ -420,6 +420,7 @@ def index():
             time_dict = {'now': now, 'boot': boot, 'start': start}
             dashboard_servers[server_id]['time_dict'] = time_dict
         else:
+            timestamp = datetime.datetime.today()
             dashboard_servers[server.id] = {}
             dashboard_servers[server.id]['online'] = False
             dashboard_servers[server.id]['name'] = server.name