Fix button is gone after dragging over 5 secs

The pending fading out animation is not canceled while dragging.
It should be canceled when the users touchs the button. If it is fading
out when the user touchs it, we should cancel the animation and set the
alpha value to 1.

Bug: 175194712
Test: atest MagnificationModeSwitchTest
      manually test
Change-Id: I3dec8520e90db7aff1050924be4e3bab1e27f23d