Fix test-regress-GH-819

Problem was exposed in 12798c6.

lib/net_uv.js

@@ -483,6 +483,11 @@ Socket.prototype.connect = function(port /* [host], [cb] */) {
   } else if (typeof host == 'string') {
     debug("connect: find host " + host);
     require('dns').lookup(host, function(err, ip, addressType) {
+      // It's possible we were destroyed while looking this up.
+      // XXX it would be great if we could cancel the promise returned by
+      // the look up.
+      if (!self._connecting) return;
+
       if (err) {
         // net.createConnection() creates a net.Socket object and
         // immediately calls net.Socket.connect() on it (that's us).