mina.js resume function fix

Resolved an issue where animations were not resume when the resume function was being called. This was done by calling the requestAnimatinFrame function at the end of the method if not other animations were being rune.

Also added a zero check to the pdif variable in the resume method that will allow the animation to resume in the instance that it was paused immediately after being created.

See the following issue for the initial post: https://github.com/adobe-webplatform/Snap.svg/issues/139