Fix race condition related to watching DGL games.

It's possible for a dgamelaunch game to end and cause rlgwebd to stop watching
it before rlgwebd has started watching it.

rlgwebd

@@ -418,6 +418,8 @@ DglSession.prototype.notifier = function (ev, finame) {
 };
 
 DglSession.prototype.close = function () {
+  /* The watcher might not be open yet. */
+  if ("recwatcher" in this)
     this.recwatcher.close();
   /* Ensure all data is handled before quitting. */
   this.startchunk();