Testing if the dropdown is opened before call positionDropdown

Even with a closed container within the orientation, resizing and scrolling events, the positionDropdown was called, showing the container although closed.

To reproduce, I record a screencast (*sorry for my poor english*).

https://www.youtube.com/watch?v=bdY2AM0i_Ck

**Browsers tested**: Chrome 34.0.1847.116, Firefox 28.0

\*please, if you can, ignore the first commit, 3f43f45. There was a logical error.