Use view handler for boundary callbacks

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

@@ -85,9 +85,7 @@ public class BoundaryCallbackMessages extends PagedList.BoundaryCallback<TupleMe
     private int pageSize;
 
     private IBoundaryCallbackMessages intf;
-
     private Handler handler;
-
     private State state;
 
     private static final int SEARCH_LIMIT_DEVICE = 1000;
@@ -111,9 +109,9 @@ public class BoundaryCallbackMessages extends PagedList.BoundaryCallback<TupleMe
         this.pageSize = pageSize;
     }
 
-    void setCallback(IBoundaryCallbackMessages intf) {
+    void setCallback(IBoundaryCallbackMessages intf, Handler handler) {
-        this.handler = new Handler();
         this.intf = intf;
+        this.handler = handler;
         this.state = new State();
     }
 

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

@@ -4331,7 +4331,7 @@ public class FragmentMessages extends FragmentBase implements SharedPreferences.
                 getContext(), getViewLifecycleOwner(),
                 viewType, type, account, folder, thread, id, filter_archive, criteria, server);
 
-        vmodel.setCallback(getViewLifecycleOwner(), callback);
+        vmodel.setCallback(getViewLifecycleOwner(), callback, view.getHandler());
         vmodel.setObserver(getViewLifecycleOwner(), observer);
     }
 

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

@@ -23,6 +23,7 @@ import android.content.Context;
 import android.content.SharedPreferences;
 import android.os.Build;
 import android.os.Bundle;
+import android.os.Handler;
 import android.text.TextUtils;
 import android.util.Pair;
 
@@ -516,9 +517,9 @@ public class ViewModelMessages extends ViewModel {
             this.boundary = boundary;
         }
 
-        void setCallback(LifecycleOwner owner, BoundaryCallbackMessages.IBoundaryCallbackMessages callback) {
+        void setCallback(LifecycleOwner owner, BoundaryCallbackMessages.IBoundaryCallbackMessages callback, Handler handler) {
             if (boundary != null) {
-                boundary.setCallback(callback);
+                boundary.setCallback(callback, handler);
 
                 owner.getLifecycle().addObserver(new LifecycleObserver() {
                     @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)