Set the currentFraction in onAnimationStart

In case of the IME being visible and requested again, there can be a case where in between onAnimationStart and calling the updateListener, the frame is rendered. In this case, the alpha value will initially be set to zero, which results in a flicker. In this case, the currentFraction of the animation was set before (due to seek=true), therefore this value should be used in onAnimationStart instead of startY (which is equal to hiddenY in the show case).

Test: manual
Fix: 329511061
Fix: 331730180
Change-Id: I52c9e340825adbe4a87111f209dbb8365c1bebd0