Fix embed link when beginning of line

Embed link function has a bug when beginning of line.
* before
![kandan](https://cloud.githubusercontent.com/assets/235329/4965734/09fcec68-6793-11e4-9f7a-8271c68c13ec.png)
* after
![kandan](https://cloud.githubusercontent.com/assets/235329/4965733/01e2af90-6793-11e4-9910-22031e3cae1e.png)