make destroySoon noop after first call

Author: arturgawlik

lib/net.js

@@ -793,23 +793,22 @@ function onReadableStreamEnd() {
   }
 }
 
-
 Socket.prototype.destroySoon = function() {
-  if (this.writable)
-    this.end();
+  if (this.destroyingOnFinish) return;
+
+  if (this.writable) this.end();
 
-  if (this.writableFinished)
+  if (this.writableFinished) {
     this.destroy();
-  else if (!this._destroyingOnFinish) {
-    this._destroyingOnFinish = true;
+  } else {
+    this.destroyingOnFinish = true;
     this.once('finish', () => {
-      this._destroyingOnFinish = false;
+      this.destroyingOnFinish = false;
       this.destroy();
     });
   }
 };
 
-
 Socket.prototype._destroy = function(exception, cb) {
   debug('destroy');