Fix bug in reader's current position

app/src/main/java/eu/kanade/mangafeed/ui/viewer/VerticalViewer.java

@@ -60,7 +60,6 @@ public class VerticalViewer extends BaseViewer {
     @Override
     public void onPageListReady(List<Page> pages) {
         adapter.setPages(pages);
-        updatePageNumber();
     }
 
     @Override

app/src/main/java/eu/kanade/mangafeed/ui/viewer/base/BaseViewer.java

@@ -29,6 +29,10 @@ public abstract class BaseViewer {
         return viewerPosition;
     }
 
+    public int getCurrentPosition() {
+        return getCurrentPageIndex(currentPosition);
+    }
+
     public abstract int getTotalPages();
     public abstract void setSelectedPage(int pageNumber);
     public abstract void onPageListReady(List<Page> pages);

app/src/main/java/eu/kanade/mangafeed/ui/viewer/base/ViewPagerViewer.java

@@ -54,6 +54,7 @@ public abstract class ViewPagerViewer extends BaseViewer {
                 onLastPageOut();
             }
         });
+        viewPager.setOnChapterSingleTapListener(activity::onCenterSingleTap);
     }
 
     public ReaderViewPager getViewPager() {
@@ -73,7 +74,6 @@ public abstract class ViewPagerViewer extends BaseViewer {
     @Override
     public void onPageListReady(List<Page> pages) {
         adapter.setPages(pages);
-        updatePageNumber();
     }
 
     @Override