handle dragging the scrollbar at empty folders

app/src/main/kotlin/com/simplemobiletools/filemanager/fragments/ItemsFragment.kt

@@ -147,7 +147,8 @@ class ItemsFragment : Fragment(), ItemsAdapter.ItemOperationsListener, Breadcrum
                     }
                     items_fastscroller.allowBubbleDisplay = context.config.showInfoBubble
                     items_fastscroller.setViews(items_list, items_swipe_refresh) {
-                        items_fastscroller.updateBubbleText(storedItems[it].getBubbleText())
+                        val item = storedItems.getOrNull(it)
+                        items_fastscroller.updateBubbleText(item?.getBubbleText() ?: "")
                     }
                 } else {
                     (currAdapter as ItemsAdapter).updateItems(storedItems)