show error if no options are selected

password.html

@@ -80,6 +80,10 @@
       };
       function outputGeneratedPassword() {
         var password = passwordGenerator.generatePassword(getOptions());
+        if (password === '') {
+          alert("Whops. You unselected all the options. I don't know what characters you want. Click on the button entitled \"Advanced Options\" and enable some options and thent try again. Nice one");
+          return;
+        }
         $("#password-input").val(password);
       }
       $(function() {