Fix crash when outbound connection fails

In node 22 atleast, network code has started returning AggregateError.
This means that when socket connection fails, err.message is an empty string.
The on('error') handler as a result invoked callback('', null) . Since error
is falsy, code assumes socket is valid and crashes.

Code is changed to always return a error string.

Fixes #3455

Author: gramakri

Changes.md

@@ -4,6 +4,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Unreleased
 
+- fix(outbound): in outbound, fix a crash when socket connection errors #3456
+
 ### [3.1.0] - 2025-01-30
 
 #### Changes

outbound/client_pool.js

@@ -32,7 +32,7 @@ exports.get_client = function (mx, callback) {
         socket.end();
         socket.removeAllListeners();
         socket.destroy();
-        callback(err.message, null);
+        callback(err ? `socket error to ${socket.name}: ${err.message} ${err.code}` : null, null);
     })
 
     socket.once('timeout', () => {