Prevent crash

app/src/main/java/eu/faircode/email/ViewModelMessages.java

@@ -625,8 +625,10 @@ public class ViewModelMessages extends ViewModel {
                 owner.getLifecycle().addObserver(new LifecycleObserver() {
                     @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
                     public void onDestroyed() {
-                        boundary.destroy(state);
+                        if (boundary != null) {
-                        boundary = null;
+                            boundary.destroy(state);
+                            boundary = null;
+                        }
                         owner.getLifecycle().removeObserver(this);
                     }
                 });