Chek if getContext() is instanceOf CategoryImagesCallback and only then request more images

Author: kbhardwaj123

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

@@ -329,7 +329,7 @@ public void onPageScrolled(int i, float v, int i2) {
             Timber.d("Returning as activity is destroyed!");
             return;
         }
-        if (i+1 >= adapter.getCount())
+        if (i+1 >= adapter.getCount() && getContext() instanceof CategoryImagesCallback)
             ((CategoryImagesCallback) getContext()).requestMoreImages();
 
         getActivity().invalidateOptionsMenu();