Don't allow focus on ReaderNavigationOverlayView (maybe fixes #5555)

app/src/main/res/layout/reader_activity.xml

@@ -37,6 +37,7 @@
         android:id="@+id/navigation_overlay"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
+        android:focusable="false"
         android:visibility="gone" />
 
     <FrameLayout