Fixes removeChild() on placeholder not in the DOM

If the Medium instance already has content when created, the placeholder will not be in the DOM and so cannot be removed. Causes the following error:


![screenshot 2014-08-07 12 05 59](https://cloud.githubusercontent.com/assets/319152/3847483/54fa3a3e-1e66-11e4-9d1b-c9fcab575638.png)