fix crash in TimelineFragment

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

@@ -206,6 +206,9 @@ public class TimelineFragment extends SFragment implements
                 || kind == Kind.LIST) {
             hashtagOrId = arguments.getString(HASHTAG_OR_ID_ARG);
         }
+
+        adapter = new TimelineAdapter(dataSource, this);
+
     }
 
     @Override
@@ -218,9 +221,6 @@ public class TimelineFragment extends SFragment implements
         progressBar = rootView.findViewById(R.id.progress_bar);
         nothingMessageView = rootView.findViewById(R.id.nothing_message);
 
-        adapter = new TimelineAdapter(dataSource, this);
-
-
         setupSwipeRefreshLayout();
         setupRecyclerView();
         updateAdapter();
@@ -835,6 +835,7 @@ public class TimelineFragment extends SFragment implements
     }
 
     private void onFetchTimelineFailure(Exception exception, FetchEnd fetchEnd, int position) {
+        if(isAdded()) {
             swipeRefreshLayout.setRefreshing(false);
 
             if (fetchEnd == FetchEnd.MIDDLE && !statuses.get(position).isRight()) {
@@ -852,6 +853,7 @@ public class TimelineFragment extends SFragment implements
             fulfillAnyQueuedFetches(fetchEnd);
             progressBar.setVisibility(View.GONE);
         }
+    }
 
     private void fulfillAnyQueuedFetches(FetchEnd fetchEnd) {
         switch (fetchEnd) {
@@ -1055,12 +1057,14 @@ public class TimelineFragment extends SFragment implements
     private final ListUpdateCallback listUpdateCallback = new ListUpdateCallback() {
         @Override
         public void onInserted(int position, int count) {
+            if(isAdded()) {
                 adapter.notifyItemRangeInserted(position, count);
                 Context context = getContext();
                 if (position == 0 && context != null) {
                     recyclerView.scrollBy(0, Utils.dpToPx(context, -30));
                 }
             }
+        }
 
         @Override
         public void onRemoved(int position, int count) {