Fix ASAN build

sapi/cli/php_cli_server.c

@@ -2535,6 +2535,8 @@ static zend_result php_cli_server_recv_event_read_request(php_cli_server *server
 			return SUCCESS;
 		EMPTY_SWITCH_DEFAULT_CASE();
 	}
+	/* Under ASAN the compiler somehow doesn't realise that the switch block always returns */
+	return FAILURE;
 } /* }}} */
 
 static zend_result php_cli_server_send_event(php_cli_server *server, php_cli_server_client *client) /* {{{ */