Fix null exception when switching dark/light theme mode with the rotation dialog popup

Test: Manually
Fixes: 159183077
Change-Id: I19891febb1b00461b6be4678a9515de483df313f
diff --git a/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java b/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
index f93f68b..2fee8f1 100755
--- a/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
+++ b/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
@@ -622,7 +622,13 @@
 
     @Override
     public void onStartRotationDialogDismiss(@NonNull DialogInterface dialog) {
-        mBottomActionBar.deselectAction(ROTATION);
+        // TODO(b/159310028): Refactor fragment layer to make it able to restore from config change.
+        // This is to handle config change with StartRotationDialog popup,  the StartRotationDialog
+        // still holds a reference to the destroyed Fragment and is calling
+        // onStartRotationDialogDismissed on that destroyed Fragment.
+        if (mBottomActionBar != null) {
+            mBottomActionBar.deselectAction(ROTATION);
+        }
     }
 
     @Override