Fix unhandled error during client connection

Client actions utilizing an EventEmitter may generate unhandled errors,
especially during initial connection.  Tracking whether the emitter has
been sent via callback is critical for proper routing of such errors.

Fix mcavage/node-ldapjs#144

lib/client/client.js

@@ -757,14 +757,20 @@ Client.prototype._send = function _send(message, expect, emitter, callback) {
   var log = this.log;
   var self = this;
   var timer = false;
+  var sentEmitter = false;
 
   if (!conn)
     return callback(new ConnectionError('no socket'));
 
   function _done(event, obj) {
     if (emitter) {
-      if (event === 'error')
+      if (event === 'error') {
+        // Error will go unhandled if emitter hasn't been sent via callback.
+        // Execute callback with the error instead.
+        if (!sentEmitter)
+          return callback(obj);
         emitter.removeAllListeners('end');
+      }
       if (event === 'end')
         emitter.removeAllListeners('error');
 
@@ -878,6 +884,7 @@ Client.prototype._send = function _send(message, expect, emitter, callback) {
       conn.unbindMessageID = message.id;
       conn.end();
     } else if (emitter) {
+      sentEmitter = true;
       return callback(null, emitter);
     }
     return false;