add empty addservers test

Author: ZNeumann

tests/integration/memcached/test_add_servers.php

@@ -31,4 +31,5 @@
                        array("host1", 1),
                        array("host2", 2),
                        array("host3", 11211)));
+$memcached->addServers(array());
 $memcached->quit();