Add null check to onTransitionMerged

Checks to see if mTransitionPausingRelayout is null before comparing it
to the merged transition IBinder.

Bug: 276973868
Test: Manual Testing
Change-Id: I772a2dfa4c29c0a78b09c2c1c7f0a5a790795604
diff --git a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
index f998217..7e178d3 100644
--- a/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
+++ b/libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java
@@ -197,7 +197,7 @@
 
     @Override
     public void onTransitionMerged(@NonNull IBinder merged, @NonNull IBinder playing) {
-        if (mTransitionPausingRelayout.equals(merged)) {
+        if (merged.equals(mTransitionPausingRelayout)) {
             mTransitionPausingRelayout = playing;
         }
     }