Update CCArmatureAnimation.cpp

it's for animation "broken body" problem.when ths animation completed , but the update of animation is still running,because of the single frame special case.we should set a condition that the animation has completed couldn't run again.
I remember i had already fixed this problem before, could you test it in latest version.
If still has problem, could you send your test to me by email?

kaile.yin@chukong-inc.com

Thanks!