Set alpha to 1 if not using alpha animation

For multi-activity PiP a new task is created, which triggers TO_FRONT
transition request that sets the alpha to 0. Since we are using bounds
animation in 3 button nav on Home press, we need to reset that alpha
to be 1 again.

Bug: 286183129
Test: manually, see http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/cQ7FF3EarUUS2W14W9M806
Change-Id: I197de8d24186850e76eb1ec5ee7a713079ff109e