Make it trigger 'chosen:showing_dropdown' event only after li fields are populated

This fixes the timing of the showing_dropdown event to only trigger after the inner LI's are created. This is a bug for users who want to add additional styling such as images inside the lists or any other type of stylings.

A JSFIDDLE was created to demonstrate the bug http://jsfiddle.net/lagrz/3A5jq/