A bad assertion snuck in with #6202. When calling view.animate() with duration: 0, view.getAnimating() is true if called in the same millisecond as view.animate() (because (0 / 0 >= 1) === false). However, it is false if called in the next millisecond (because (1 / 0 >= 1) === true). We don't want to be testing whether a these calls occur in the same millisecond.
(0 / 0 >= 1) === false
(1 / 0 >= 1) === true
In addition to removing this bad assertion, this more explicitly guards against division by zero (treating zero duration animations as immediately complete).
Stop asserting that zero duration animations take time
Stop dividing by zero