Pausing and then immediately playing an animation causes frame without effect

[ewilligers]

Executing the following code midway through an animation causes a single frame where no animation effect is applied.
animation.pause();
animation.play();

play() calls _ensureAlive(), which executes
this._inEffect = this._effect._update(this.currentTime)
However, this._currentTimePending is true, so get currentTime() returns null instead of this._currentTime.