Stop scanning for prev/next on destroy

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

@@ -21,4 +21,11 @@ package eu.faircode.email;
 
 public class ObjectHolder<T> {
     public T value;
+
+    public ObjectHolder() {
+    }
+
+    public ObjectHolder(T init) {
+        this.value = init;
+    }
 }

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

@@ -272,6 +272,14 @@ public class ViewModelMessages extends ViewModel {
             return;
         }
 
+        ObjectHolder<Boolean> alive = new ObjectHolder<>(true);
+        owner.getLifecycle().addObserver(new LifecycleObserver() {
+            @OnLifecycleEvent(Lifecycle.Event.ON_ANY)
+            public void onAny() {
+                alive.value = owner.getLifecycle().getCurrentState().isAtLeast(Lifecycle.State.STARTED);
+            }
+        });
+
         Log.i("Observe previous/next id=" + id);
         //model.list.getValue().loadAround(lpos);
         model.list.observe(owner, new Observer<PagedList<TupleMessageEx>>() {
@@ -363,7 +371,7 @@ public class ViewModelMessages extends ViewModel {
                                     return getPair(plist, ds, count, from + j);
                         }
 
-                        for (int i = 0; i < count; i += CHUNK_SIZE) {
+                        for (int i = 0; i < count && alive.value; i += CHUNK_SIZE) {
                             Log.i("Observe previous/next load" +
                                     " range=" + i + "/#" + count);
                             List<TupleMessageEx> messages = ds.loadRange(i, Math.min(CHUNK_SIZE, count - i));