Fix windowless splash won't removed while hovering back gesture.

The windowless surface can be add after transition ready in core, so
there can defer the check until transaction applied.

Flag: EXEMPT bugfix
Bug: 372230928
Test: create windowless splash instead of snapshot, verify windowless
splash get removed as soon as prepare back transition ready.

Change-Id: I306b1d936504c48bd83d2185a54ecbddd0720d3e
diff --git a/services/core/java/com/android/server/wm/BackNavigationController.java b/services/core/java/com/android/server/wm/BackNavigationController.java
index ccd5996..49fcb18 100644
--- a/services/core/java/com/android/server/wm/BackNavigationController.java
+++ b/services/core/java/com/android/server/wm/BackNavigationController.java
@@ -1328,16 +1328,13 @@
             if (!allWindowDrawn) {
                 return;
             }
-            final SurfaceControl startingSurface = mOpenAnimAdaptor.mStartingSurface;
-            if (startingSurface != null && startingSurface.isValid()) {
-                startTransaction.addTransactionCommittedListener(Runnable::run, () -> {
-                    synchronized (mWindowManagerService.mGlobalLock) {
-                        if (mOpenAnimAdaptor != null) {
-                            mOpenAnimAdaptor.cleanUpWindowlessSurface(true);
-                        }
+            startTransaction.addTransactionCommittedListener(Runnable::run, () -> {
+                synchronized (mWindowManagerService.mGlobalLock) {
+                    if (mOpenAnimAdaptor != null) {
+                        mOpenAnimAdaptor.cleanUpWindowlessSurface(true);
                     }
-                });
-            }
+                }
+            });
         }
 
         void clearBackAnimateTarget(boolean cancel) {