Null-check AV before checking its alpha.

Bug: 159769573
Test: no crashing
Change-Id: I139091a1b4689e13b2b3337ee2988df662798204

packages/SystemUI/src/com/android/systemui/bubbles/BubbleExpandedView.java

@@ -495,12 +495,9 @@ public class BubbleExpandedView extends LinearLayout {
         }
         final float alpha = visibility ? 1f : 0f;
 
-        if (alpha == mActivityView.getAlpha()) {
-            return;
-        }
-
         mPointerView.setAlpha(alpha);
-        if (mActivityView != null) {
+
+        if (mActivityView != null && alpha != mActivityView.getAlpha()) {
             mActivityView.setAlpha(alpha);
             mActivityView.bringToFront();
         }