Fix ZMQ listen addresses check

src/config.c

@@ -126,7 +126,7 @@ int facilities_config() {
             }
         }
     }
-    if (!facilities.zmq.n_responders) {
+    if (facilities.zmq.n_responders <= 1) {
         log_info("[config] a valid address to listen to was not found, exiting now");
         rv = 1;
         goto cleanup;