Protect against ImageView changing to a null Drawable during Transition.
Protect against ImageView changing to a null Drawable during Transition.

Bug 17600191

Change-Id: I5918866dbb6594725f4712a92acdef23003e8f3e

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base