Framework Support Library: Ensure addSharedElement on TransitionHelper
is only called on non-null views

Prior to this, the null check was performed within the
TransitionHelper's addSharedElement itself. Removed and transferred the
null checking to the actual users of this method in GuidedStepFragment.

Change-Id: I40def6c588364847edbbb30666b3e55f3f75dc52
2 files changed