updated close function for safety

Author: unilaterus

Diff for: lib/http-proxy/index.js

@@ -134,8 +134,16 @@ ProxyServer.prototype.listen = function(port, hostname) {
 
 ProxyServer.prototype.close = function(callback) {
   if (this._server) {
-    this._server.close(callback);
-    this._server = null;
+    // Wrap callback to nullify server after all open connections are closed.
+    var callback_wrapper = function() {
+        this._server = null;
+
+        if (callback) {
+            callback(arguments);
+        }
+    };
+
+    this._server.close(callback_wrapper);
   }
 };