Prevent multiple registrations to eventHub on same TimelineFragment (#879)

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

@@ -119,6 +119,7 @@ public class TimelineFragment extends SFragment implements
     public TimelineCases timelineCases;
     @Inject
     public EventHub eventHub;
+    private boolean eventRegistered = false;
 
     private SwipeRefreshLayout swipeRefreshLayout;
     private RecyclerView recyclerView;
@@ -378,6 +379,7 @@ public class TimelineFragment extends SFragment implements
         }
         recyclerView.addOnScrollListener(scrollListener);
 
+        if (!eventRegistered) {
             eventHub.getEvents()
                     .observeOn(AndroidSchedulers.mainThread())
                     .as(autoDisposable(from(this, Lifecycle.Event.ON_DESTROY)))
@@ -413,6 +415,8 @@ public class TimelineFragment extends SFragment implements
                             handleStatusComposeEvent(status);
                         }
                     });
+            eventRegistered = true;
+        }
     }
 
     @Override