Addendum to commit 30d7f269de to cancel the callbacks so they're not called after the fragment is detached. Closes #357

app/src/main/java/com/keylesspalace/tusky/fragment/ViewMediaFragment.java

@@ -138,7 +138,7 @@ public class ViewMediaFragment extends BaseFragment {
 
                         @Override
                         public void onError() {
-                            // if there's no image in cache, load from network and start trnasition
+                            // if there's no image in cache, load from network and start transition
                             // immediately.
                             photoActionsListener.onBringUp();
 
@@ -153,6 +153,13 @@ public class ViewMediaFragment extends BaseFragment {
         return rootView;
     }
 
+    @Override
+    public void onDetach() {
+        super.onDetach();
+        Picasso.with(getContext())
+                .cancelRequest(photoView);
+    }
+
     private void loadImageFromNetwork(String url, ImageView photoView) {
         Picasso.with(getContext())
                 .load(url)