Null reference to split callback

Bug: 302551868
Test: Ran atest NexusLauncherTests:com.android.quickstep.TaplTestsSplitscreen
which caused some regressions last time. Passed locally

Change-Id: I94b28296cf12c5087ee3e878352c057d1d1a73de
diff --git a/quickstep/src/com/android/quickstep/util/SplitSelectStateController.java b/quickstep/src/com/android/quickstep/util/SplitSelectStateController.java
index c8831c7..0c4fcf9 100644
--- a/quickstep/src/com/android/quickstep/util/SplitSelectStateController.java
+++ b/quickstep/src/com/android/quickstep/util/SplitSelectStateController.java
@@ -590,7 +590,7 @@
 
         private final int mInitialTaskId;
         private final int mSecondTaskId;
-        private final Consumer<Boolean> mSuccessCallback;
+        private Consumer<Boolean> mSuccessCallback;
 
         RemoteSplitLaunchTransitionRunner(int initialTaskId, int secondTaskId,
                 @Nullable Consumer<Boolean> callback) {
@@ -617,6 +617,7 @@
                             finishAdapter.run();
                             if (mSuccessCallback != null) {
                                 mSuccessCallback.accept(true);
+                                mSuccessCallback = null;
                             }
                             resetState();
                         });