linear animateMotion and zero path length
A path with several path fragments of zero length is used for a
linear animateMotion of a blue square. The path is given in gray,
some simpler animateMotion elements are used to perform the same
motion for a red square exactly below the blue one.
If something red gets visible, an error is occured.
calcMode linear
red: animateMotion calcMode linear using values
blue: animateMotion calcMode linear