throwing badly named exception when selector matches no resutls.

[bzmw]

The current version of prettyCheckable throws an exception that doesn't really make a lot of sense when the selector doesn't match anything found in the DOM.
On my project I have added the following to stop it from throwing exceptions.

       instance = this.data( dataPlugin );

 +        if (!instance) {
 +          console.warn("prettyCheckable: Selector returned no results");
 +          return;
 +        }
 +
          instance.element = this;

[arthurgouveia]

Wouldn't you consider making a PR?