net: check status code in afterWrite

Fixes memory leak and spin on writing to dead fds. This was tested in
production.

lib/net.js

@@ -465,7 +465,11 @@ function afterWrite(status, handle, req, buffer) {
   if (self.destroyed) {
     return;
   }
-  // TODO check status.
+
+  if (status) {
+    self.destroy(errnoException(errno, 'write'));
+    return;
+  }
 
   timers.active(this);