Ensure FlxSprite's animation has the right angle.

When we have a FlxPrerotatedAnimation, it used to have its angle lag
behind until the next update() call, both for the initial value of
FlxSprite.angle, and for any updates to it.

This prepopulates the FlxPrerotatedAnimation.angle, and makes sure to
call FlxAnimationController's update().

Fixes #1395.
Merge pull request #1396 from jorgenpt/immediately-update-prebaked-rotation-angle

Ensure FlxSprite's animation has the right angle.