Use more accurate check for isInPreviewStage

The previous logic sometimes flickered to false during the final frame of the cancel animation.

Bug: 350705972
Test: Manual, i.e. testing on device in Flexiglass
Flag: com.android.systemui.scene_container
Change-Id: Ic6024a6ca730736a13e4606279e0539213c33b06
1 file changed