Detach children in transaction.

Trivial error.

Bug: 79441653
Test: Manual
Change-Id: I8fcc60aa2b8bb44593a2e5ada2f7c0c8a08cc16a

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

@@ -919,10 +919,12 @@ class AppWindowToken extends WindowToken implements WindowManagerService.AppFree
     }
 
     void detachChildren() {
+        SurfaceControl.openTransaction();
         for (int i = mChildren.size() - 1; i >= 0; i--) {
             final WindowState w = mChildren.get(i);
             w.mWinAnimator.detachChildren();
         }
+        SurfaceControl.closeTransaction();
     }
 
     void finishRelaunching() {