When invoking manually, make sure the $ selection is not empty

I was just checking to see what happens when invoking the modal manually, and I used the $('#sticky') example from examples. As we don't have a #sticky element in the DOM, the modal just display the blocker.

jquery.modal.js

@@ -118,7 +118,7 @@
  };
 
  $.fn.modal = function(options){
- new $.modal(this, options);
+ if(this.length === 1) { new $.modal(this, options); }
  return this;
  };