Check if RemoteAnimationTargets apps are present

* Before the refactor to use RemoteTargetGluer,
we only set the preview if the runningTaskTarget wasn't
null, that check got removed during the refactor.
* Why that check was there to begin with is a bit
of a mystery, sadly

Fixes: 199658495
Change-Id: I053fac0fa0eee0979dff651c01287d04d06298e6