tools: cleanup our clients in the eis demo server

Where we're interrupted before a disconnect event from the client, we
would leave the demo client hanging. This upsets valgrind.

tools/eis-demo-server.c

@@ -625,5 +625,10 @@ int main(int argc, char **argv)
 		}
 	}
 
+	struct eis_demo_client *democlient;
+	list_for_each_safe(democlient, &server.clients, link) {
+		eis_demo_client_unref(democlient);
+	}
+
 	return 0;
 }