* grub-core/gfxmenu/gui_list.c (draw_scrollbar): Fixed rare

occasional bug. If there are too many boot entries or too low
       scrollbar height then we need to use another formula to calculate
       the position and size of the scrollbar thumb.

grub-core/gfxmenu/gui_list.c

@@ -219,6 +219,13 @@ draw_scrollbar (list_impl_t self,
                            tracklen);
   int thumby = tracktop + tracklen * (value - min) / (max - min);
   int thumbheight = tracklen * extent / (max - min) + 1;
+  /* Rare occasion: too many entries or too low height. */
+  if (thumbheight < thumb_vertical_pad)
+    {
+      thumbheight = thumb_vertical_pad;
+      thumby = tracktop + ((tracklen - thumb_vertical_pad) * (value - min)
+                           / (max - extent));
+    }
   thumb->set_content_size (thumb,
                            scrollbar_width - frame_horizontal_pad
                            - thumb_horizontal_pad,