Fixes #3705 (Crash when viewing pic I just uploaded) (#3782)

* Fixes #3705
* Let the MediaDetailPager fragment know when the contributions have been updated

* Handle NPE, null check on adapter in MediaDetailPagerFragment

app/src/main/java/fr/free/nrw/commons/contributions/ContributionsFragment.java

@@ -224,6 +224,14 @@ public class ContributionsFragment
                 Timber.d("Fetching thumbnail for %s", contribution.filename);
                 contributionsPresenter.fetchMediaDetails(contribution);
             }
+
+            @Override
+            public void onContributionsUpdated() {
+                //If the contributions are updated, let the pager fragment know
+                if (null != mediaDetailPagerFragment) {
+                    mediaDetailPagerFragment.notifyDataSetChanged();
+                }
+            }
         });
 
         if(null==mediaDetailPagerFragment){

app/src/main/java/fr/free/nrw/commons/contributions/ContributionsListAdapter.java

@@ -77,5 +77,7 @@ public class ContributionsListAdapter extends RecyclerView.Adapter<ContributionV
         Contribution getContributionForPosition(int position);
 
         void fetchMediaUriFor(Contribution contribution);
+
+        void onContributionsUpdated();
     }
 }

app/src/main/java/fr/free/nrw/commons/contributions/ContributionsListFragment.java

@@ -188,6 +188,7 @@ public class ContributionsListFragment extends CommonsDaggerSupportFragment {
         this.contributions.clear();
         this.contributions.addAll(contributionList);
         adapter.setContributions(contributions);
+        callback.onContributionsUpdated();
     }
 
     public interface SourceRefresher {

app/src/main/java/fr/free/nrw/commons/media/MediaDetailPagerFragment.java

@@ -320,7 +320,9 @@ public class MediaDetailPagerFragment extends CommonsDaggerSupportFragment imple
      * The method notify the viewpager that number of items have changed.
      */
     public void notifyDataSetChanged(){
-        adapter.notifyDataSetChanged();
+        if (null != adapter) {
+            adapter.notifyDataSetChanged();
+        }
     }
 
     @Override