Don't trust convexity when applying transforms.
    
    In theory, a convex shape transformed by an affine matrix should still
    be convex. However, due to numerical imprecision of floats, when we try
    to determine if something is convex, we can get different answers pre
    and post a transformation (think of two line segments nearly co-linear).
    
    Convex paths take a faster scan converter, but it is only well behaved
    if the path is, in fact, convex. Thus we have to be conservative about
    which paths we mark as convex, and cant's trust transformed paths to
    retain their convexity. We re-calculate when a transform is applied.