Fix NPE on TaskFragment

We need to deregister the WindowContainerListener at an
earlier stage to avoid a translucent activity to have a
reference to an opaque one without a parent TaskFragment
which causes getTaskFragment() to return null.

Fixes: 278899220
Test: atest WmTests:SizeCompatTests

Change-Id: I06bef5f386cffdc7e89e7e39bd33b1eb3c0ff6b8

services/core/java/com/android/server/wm/ActivityRecord.java

@@ -4281,6 +4281,7 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
 
         mTaskSupervisor.getActivityMetricsLogger().notifyActivityRemoved(this);
         mTaskSupervisor.mStoppingActivities.remove(this);
+        mLetterboxUiController.destroy();
         waitingToShow = false;
 
         // Defer removal of this activity when either a child is animating, or app transition is on
@@ -4350,8 +4351,6 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
             mWmService.updateFocusedWindowLocked(UPDATE_FOCUS_NORMAL, true /*updateInputWindows*/);
         }
 
-        mLetterboxUiController.destroy();
-
         if (!delayed) {
             updateReportedVisibilityLocked();
         }

services/tests/wmtests/src/com/android/server/wm/SizeCompatTests.java

@@ -406,7 +406,6 @@ public class SizeCompatTests extends WindowTestsBase {
         clearInvocations(translucentActivity.mLetterboxUiController);
 
         // We destroy the first opaque activity
-        mActivity.setState(DESTROYED, "testing");
         mActivity.removeImmediately();
 
         // Check that updateInheritedLetterbox() is invoked again