Fixed: EZP-23251 Javascript error trying to paste an iframe html in a li...

...teral html tag

Fixes https://jira.ez.no/browse/EZP-23251

Description there says it all. I was getting a javascript error when trying to paste an iframe inside a literal tag with html class

Here is my approach. But to be honest, looks more like a workaround than a proper fix... Thoughts?